Mudflats or mud flats, also known as tidal flats, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A recent global analysis suggested they are as extensive globally as mangroves. [1] They are found in sheltered areas such as bays, bayous, lagoons, and estuaries. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and marine animal detritus. Most of the sediment within a mudflat is within the intertidal zone, and thus the flat is submerged and exposed approximately twice daily.

In the past tidal flats were considered unhealthy, economically unimportant areas and were often dredged and developed into agricultural land.[2] Several especially shallow mudflat areas, such as the Wadden Sea, are now popular among those practising the sport of mudflat hiking.

On the Baltic Sea coast of Germany in places, mudflats are exposed not by tidal action, but by wind-action driving water away from the shallows into the sea. These wind-affected mudflats are called windwatts in German.

Tidal flat general sketch
General sketch-map of a tidal plain, showing the typical tripartition in supratidal, intertidal and subtidal zones. The most apparent character of the area is the development of tidal channels, affecting mainly the intertidal zone. In this case, the tidal flat is protected seaward by a beach barrier, but in many cases (low-energy waves and longshore currents) the tidal flats may directly pass into a shallow marine environment.


Stewart Island Oban Mudflats
Mudflats near Oban on Stewart Island, New Zealand

Tidal flats, along with intertidal salt marshes and mangrove forests, are important ecosystems.[3] They usually support a large population of wildlife, and are a key habitat that allows tens of millions of migratory shorebirds to migrate from breeding sites in the northern hemisphere to non-breeding areas in the southern hemisphere. They are often of vital importance to migratory birds, as well as certain species of crabs,[4] mollusks and fish.[5] In the United Kingdom mudflats have been classified as a Biodiversity Action Plan priority habitat.

The maintenance of mudflats is important in preventing coastal erosion. However, mudflats worldwide are under threat from predicted sea level rises, land claims for development, dredging due to shipping purposes, and chemical pollution.[1] In some parts of the world, such as East and South-East Asia, mudflats have been reclaimed for aquaculture, agriculture, and industrial development. For example, around the Yellow Sea region of East Asia, more than 65% of mudflats present in the early 1950s had been destroyed by the late 2000s.[6][7] It is estimated that up to 16% of the world tidal flats have disappeared since the mid-1980s. [1]

Mudflat sediment deposits are focused into the intertidal zone which is composed of a barren zone and marshes. Within these areas are various ratios of sand and mud that make up the sedimentary layers.[8] The associated growth of coastal sediment deposits can be attributed to rates of subsidence along with rates of deposition (example: silt transported via river) and changes in sea level.[8]

Barren zones extend from the lowest portion of the intertidal zone to the marsh areas. Beginning in close proximity to the tidal bars, sand dominated layers are prominent and become increasingly muddy throughout the tidal channels. Common bedding types include laminated sand, ripple bedding, and bay mud. Bioturbation also has a strong presence in barren zones.

Marshes contain an abundance of herbaceous plants while the sediment layers consist of thin sand and mud layers. Mudcracks are a common as well as wavy bedding planes.[8] Marshes are also the origins of coal/peat layers because of the abundant decaying plant life.[8]

Salt pans can be distinguished in that they contain thinly laminated layers of clayey silt. The main source of the silt comes from rivers. Dried up mud along with wind erosion forms silt dunes. When flooding, rain or tides come in, the dried sediment is then re-distributed.[8]

Selected example areas

Brewster mudflat
Mudflats in Brewster, Massachusetts, United States, extending hundreds of yards offshore at the low tide. The line of seashells in the foreground indicates the high-water mark.
Skagit Bay 6308
Gulls feeding on mudflats in Skagit Bay, Washington.

See also


  1. ^ a b c Murray, N.J.; Phinn, S.R.; DeWitt, M.; Ferrari, R.; Johnston, R.; Lyons, M.B.; Clinton, N.; Thau, D.; Fuller, R.A. (2019), "The global distribution and trajectory of tidal flats", Nature, 565: 222–225, doi:10.1038/s41586-018-0805-8/
  2. ^ Dredging Indian River Lagoon Wetlands 1920 - 1950s
  3. ^ Tidal flat habitats
  4. ^ Mud crab (Scylla serrata) culture in tidal flats with existing mangroves
  5. ^ Manko - Tidal Flat, Mangrove Forest
  6. ^ MacKinnon, J.; Verkuil, Y.I.; Murray, N.J. (2012), IUCN situation analysis on East and Southeast Asian intertidal habitats, with particular reference to the Yellow Sea (including the Bohai Sea), Occasional Paper of the IUCN Species Survival Commission No. 47, Gland, Switzerland and Cambridge, UK: IUCN, p. 70, ISBN 9782831712550
  7. ^ Murray, N.J.; Clemens, R.S.; Phinn, S.R.; Possingham, H.P.; Fuller, R.A. (2014), "Tracking the rapid loss of tidal wetlands in the Yellow Sea", Frontiers in Ecology and the Environment, 12 (5): 267–272, doi:10.1890/130260/
  8. ^ a b c d e Reineck, H.E, and I.B Singh, Depositional Sedimentary Environments, 2nd Ed. New York: Springer-Verlag Berlin Heidelberg, 1980, pp. 418-428

External links

Beatrice Islet Conservation Park

Beatrice Islet Conservation Park is a protected area occupying the Beatrice Islets and adjoining intertidal areas in Nepean Bay on Kangaroo Island, South Australia. It is located about 4 kilometres (2.5 miles) east of the town of Kingscote.It was dedicated in 1967 for 'conservation of wildlife habitat' replacing previous statutory protection dating back to 1909. A management philosophy for the conservation park published in 1987 supports the use of the park as a 'feeding and roosting habitat for waterbirds'. The conservation park which is about 103 ha (250 acres) in size, occupies part of a sandspit extending from Cape Rouge to the immediate north of Kingscote. The Beatrice Islets which originally supported bushes of African boxthorn which, when cleared in either the 1960s or the 1970s, resulted in erosion and destabilisation of both islets to the extent that both were described as being 'a mudflat/cocklebed' which is submerged at high water.The conservation park is classified as an IUCN Category Ia protected area.


Blauort is one of Germany's uninhabited North Sea sandy islets off the coast of Dithmarschen (near Büsum), and measures about 1,200 m from north to south and 500 metres from east to west. It is surrounded by the sandbank of Blauortsand, which is bounded to the north by the creek of the Wesselburener Loch and to the south by the Piep.

According to the Schleswig-Holstein National Park Office in Tönning, Blauort, like the sandbank of Tertius to the south, belongs to the parish of Hedwigenkoog. However, the state government of Schleswig-Holstein has not yet officially confirmed and authorised this.

The islet of Blauort is migrating steadily eastwards, like all sandy islands on the west coast of Schleswig-Holstein. From 1938 to 1962, the sand moved towards the land at a rate of about 32 metres per year and, at present, it is about six miles from the coast. Blauort's highest point lies above the average high tide (which is about 1.83 m above sea level (NN) ) and is only completely submerged by spring tides or storm surges. There is no vegetation on Blauort.

Blauort is one of the few, largely unspoilt habitats on the coast and of great importance for seabirds and common seals, Since 1985 it has been part of protection zone I in the Schleswig-Holstein Wadden Sea National Park.

Blauort is marked by a daymark, the Blauortbake ("Blauort daymark").

In the summer months, guided mudflat walks of the Blauortsand are offered which depart from Büsum and Wesselburen.

The Büsumer writer, Stefanie Bach Stein, called one of her books of poetry Blauort.

Cicindela trifasciata sigmoidea

Cicindela trifasciata sigmoidea, commonly called the mudflat tiger beetle, is a subspecies of tiger beetle.

The specimen shown in the picture was raised in captivity in Pasadena, California, an inland city. Its parents were captured at the Mugu Naval Base marsh in Ventura, California in 2003 (for a UCLA Masters thesis). This species of tiger beetle was found to be rare in 1982 by a study conducted by the Los Angeles County Natural History Museum. The leading entomologists for the 1982 study were Christopher Nagano and James Hogue. This tiger beetle, the second smallest of the six Cicindela in the Naval Base, is now extremely rare.

Diloma subrostratum

Diloma subrostratum, common name the mudflat top shell, is a species of small sea snail, a marine gastropod mollusk in the family Trochidae, the top snails.

Don Hoi Lot

Don Hoi Lot (Thai: ดอนหอยหลอด, pronounced [dɔ̄ːn hɔ̌j lɔ̀ːt]) is a sandbar off the coast of Samut Songkhram Province at the northwestern tip of the Bay of Bangkok. The sediments of the Mae Klong River together sediments from the sea form a system of mudflats, which are populated by razor clams (Solen regularis), which also gave the site its Thai name. The site has the largest population of this species, which is endemic to the northern Gulf of Thailand. Also 18 bird and 42 invertebrate species are recorded at the mudflats and the adjoining coastal mangrove forests. The mudflat Don Nai is on the coast. Nearby, the highly revered shrine of Prince Chumphon Khet-Udomsak attracts Thai visitors.

Since 5 July 2001 the site has been registered as Ramsar site number 1099. Don Hoi Lot is named after the tubular shellfish, known as razor clams or "worm shells" in English. the area covers three kilometres in width and five kilometres long in Tambon Bang Chakreng.


Finstown in the parish of Firth on Mainland, Orkney, Scotland is the fourth-largest settlement on the island. According to travel author Eric Linklater, the homes in Finstown are tidy and well cared for. This settlement is situated along the Bay of Firth, whose fringe is a shallow intertidal mudflat. Finstown is situated at the junction of the A965 and the A966. In 2011 it has a population of 440.

Frisian Islands

The Frisian Islands, also known as the Wadden Islands or the Wadden Sea Islands, form an archipelago at the eastern edge of the North Sea in northwestern Europe, stretching from the northwest of the Netherlands through Germany to the west of Denmark. The islands shield the mudflat region of the Wadden Sea (large parts of which fall dry during low tide) from the North Sea.

The Frisian Islands, along with the mainland coast in the German Bight, form the region of Frisia (German and Dutch: Friesland), homeland of the Frisian people. Generally, the term Frisian Islands is used for the islands where Frisian is spoken and the population is ethnically Frisian. In contrast, the term Wadden Islands applies to the entire archipelago, including the Dutch-speaking westernmost islands of Texel and Vlieland and Danish-speaking Danish Wadden Sea Islands further north off the west coast of Jutland.

Most of the Frisian Islands are environmentally protected areas, and an international wildlife nature reserve is being coordinated between the Netherlands, Germany and Denmark. Natural gas and oil drilling continue, however, and in the vicinity of the Ems, Weser and Elbe estuaries, and ship traffic causes tension between wildlife protection and economic values.

Glenelg River (Western Australia)

The Glenelg River is a river in the Kimberley region of Western Australia.

The headwaters of the river rise in the Elizabeth and Catherine Range. The river flows in a north-westerly direction past the Whately Range and discharges into Maitland Bay then through George Water, into Doubtful Bay and finally the Timor Sea.

The McRae River is a tributary of the Glenelg River.

The first recorded exploration of the river was made in 1838, by a party led by George Grey, but they were poorly prepared and ill-equipped. Grey named the river on 2 March 1838 after Lord Glenelg who was Secretary of State for the Colonies from 1835 to 1839 and under whose auspices Grey undertook his explorations.On 31 March 1929, en route from Sydney to England, the Southern Cross with Charles Kingsford Smith at the helm made an emergency landing on a mudflat near the mouth of the river. The Southern Cross was found and rescued after a fortnight's searching, with George Innes Beard, Albert Barunga and Wally from Kunmunya Mission the first overland party to reach the downed aircraft.

Goose Island State Park

Goose Island State Park is a state park in the U.S. state of Texas, located north of the city of Rockport on the coast of the Gulf of Mexico. The park covers 321.4 acres (130 ha). It is surrounded by both St. Charles and Aransas Bays.

The park was established on land acquired from private owners between the years 1931–35. The Civilian Conservation Corps built the earliest facilities.

The park is home to "The Big Tree", a Southern live oak (Quercus virginiana), thought to be over 1000 years old. It has a circumference of 35 feet (11 m), is 44 feet (13 m) in height and has a crown spread of 90 feet (27 m).

Although it is located on the seashore, there is no designated swimming area at the park, as the shoreline consists of concrete, oyster shell, mudflat, and marsh grass. Instead, the main park activities include camping, birding, fishing, and boating. The park averages more than 60,000 overnight campers each year and has about 200,000 visitors annually. There are 45 shade shelters with electricity and water on the island. There are 57 shelters with electricity and water, and 27 with water and no electricity. Speckled trout, redfish, drum, flounder, and sheepshead are a few of the fish caught.

Kukup Island

Kukup Island (Malay: Pulau Kukup) is an island in Pontian District, Johor, Malaysia.

Langlee Island

Langlee Island or Langley Island is an island in the Hingham Bay area of the Boston Harbor Islands National Recreation Area. The island has a permanent size of 4 acres (16,000 m2), plus an intertidal zone of a further 3 acres (12,000 m2), and is composed of a massing of Roxbury puddingstone which rises to a height of 40 feet (12 m) above sea level. This results in steep cliffs on the northern shore, while there are several small sandy beaches and a tidal mudflat on the east side. The center of the island contains glacial till that supports tree and shrub cover. As a result of previous planting, the island hosts large examples of oak, maple, juniper, and birch trees, while self-seeded huckleberry and viburnum mix with common greenbriar, dewberry, sumac, and poison ivy.The island was purchased by John Langlee in 1689, and has had several private owners since. Eventually, it was given to the town of Hingham by its last private owner, and the town still manages it as part of the National Recreation Area. Access is by private boat only.

Lilaeopsis masonii

Lilaeopsis masonii is a species of flowering plant in the carrot family known by the common names mudflat quillplant and Mason's lilaeopsis. It is endemic to California, where it is known only from the Sacramento-San Joaquin River Delta and nearby shores of San Francisco Bay.

It is a plant of freshwater and brackish marshes and other estuary habitat. The plant is rare overall, limited in distribution to about 80 populations in a single network of water bodies, but it is locally abundant in some areas. It is a common bayside plant in Suisun Marsh.It is threatened by numerous environmental factors, however, including erosion, flood control activities such as levee maintenance and dredging, consumption of marshland for development, agriculture, recreation, pollution, and competition with water hyacinth (Eichhornia crassipes).This is a small perennial herb, superficially grasslike in appearance, growing in small continuous tufts from spreading rhizomes. The thready or hairlike leaves are several centimeters high and green in color. The inflorescence is a minute, threadlike umbel of tiny greenish white to maroon flowers each yielding a spherical fruit about a millimeter wide.

Mudflat hiking

Mudflat hiking (Danish: Vadehavsvandring, Dutch: Wadlopen, West Frisian: Waadrinnen, German: Wattwandern) is a recreation enjoyed by Dutch, Germans, Danes, and others in the Netherlands, northwest Germany and in Denmark. Mudflat hikers are people who, with the aid of a tide table, use a period of low water to walk and wade on the watershed of the mudflats, especially from the Frisian mainland coast to the Frisian islands.The Wadden Sea, a belt of the North Sea, is well suited to this traditional practice. Belts of this shallow sea lie off the mainland of the Netherlands, between Friesland and the Frisian Islands; off the coast of northwestern Germany; and off the coast of southwest Jutland in Denmark.

In the Netherlands, mudflat hikers can walk from the mainland to Terschelling, Ameland, Engelsmanplaat, Schiermonnikoog, Simonszand, and Rottumeroog. Other mudflat hiking routes are known but are not recommended, either because of their inherent dangers (the correct path is difficult to follow and/or there are insufficient margins of error in timing the trip) or for the minimization of ecological disturbance, or both.

In Germany, mudflat hikers can walk to the East Frisian Islands of Norderney, Baltrum, Langeoog, Spiekeroog, Minsener-Oldoog and Neuwerk. The North Frisian Halligen Süderoog, Südfall, Oland, Langeneß, Gröde, and Nordstrandischmoor as well as the island Föhr can also be reached from the mainland. There is also a connection between the islands Amrum and Föhr. For this specific route, a guide is mandatory.

In Denmark, mudflat hikers can walk to Mandø, Fanø, and Langli.

The same activity is occasionally practiced in England, most commonly making use of abandoned sub-tidal carriage roads once used by horse-drawn traffic. The best-known example is the crossing of Morecambe Bay, where guided walks along the 11km route are led by the current holder of the ancient office of Queen's Guide to the Sands. Another is The Broomway in Essex. Both routes pose severe potential dangers and walkers are usually led by experienced guides.

Muthupet Lagoon

Muthupet Lagoon is located at the southern end of the Cauvery river delta on the Bay of Bengal, covering an area of approximately 6,803.01 ha of which only 4% is occupied by well-grown mangroves. The rivers Paminiyar, Koraiyar, Kilaithankiyar, Marakkakoraiyar and other tributaries of the river Cauvery flow through Muthupet and adjacent villages. At the tail end, they form a lagoon before meeting the sea. The northern and western borders of the lagoon are occupied by muddy silt ground which is devoid of mangroves. The mangroves beyond Muthupet lagoon are discontinuously found along the shore and extended up to Point Calimere. Muthupet mangrove forest was under the control of Chatram Department from 1853 to 1912 (Chengappa, 1918). The Government of the Presidency of Madras Gazette (1937) shows, from 1923 to 1936, half of the revenue obtained from selling mangrove products was paid to the revenue department and the remaining half was spent to maintain the “Chatrams” (Charity homes). The Government declared the Muthupet mangrove forest as revenue forest in February 1937 and accordingly the mangrove forest was handed over to the forest department of the Madras Presidency.

The forest is maintained by Tamil Nadu Forest Department. The entire mangrove forest is divided into Palanjur reserve forest, Thamarankottai reserve forest, Maravakkadu reserve forest, Vadakadu reserve forest, Thuraikadu reserve forest and Muthupet reserve forest.

The word 'lagoon' refers to the shallow salt or brackish water body that lies close to the sea. Muthupet reserve forest covers the lagoon, river creeks and the mudflats. Muthupet (mullipallam) Lagoon is a spectacular natural creation, which is 8 km from nearby Muthupet town and can be reachable only by boat. The lagoon is shallow with the average of 1m depth. The bottom of the lagoon is formed of silt clay substratum. The tidal fluctuations can be observed well with the exposure of oyster beds and roots during low tide.

The tidal fluctuations are playing a major role in dispersing the mangrove seeds. Dense mangroves mostly cover the lagoon shore. The islets are found on western side which are submerged during high tide. The salinity is the major environmental factor, controlling zonation of Muthupet mangrove forest. Avicennia marina is the conqueror of the forest which is found as a single dominant species.

Southern side (mud flat) separates the lagoon from adjacent sea that also leaves a permanent mouth of lagoon with seasonally opened shallow waterways. The width of mudflat is increased from lagoon mouth to the eastern direction. The mudflat looks like a desert in summer, but the presence of dead gastropods under the surface soil layer and the erosion of soil at the centre of mudflat reveal the submergence of mudflat during flood. There is a difference between the lagoon shore and seashore of the same mudflat, in the aspect of distance of mangroves from fluctuating water level.

The mangroves have grown close to water level in lagoon side but not in seashore. The reason may be the difference in the nature of fine clayey silt deposition that carried by the rivers. The salt marshes are found as under herb as well as lining the inner side of the forest. In the degraded central part of the mudflat, the soft fine silt is found only around the salt marshes. But, the remaining barren ground is hard (clay) which may due to the erosion of surface silt by wind or floodwater. Thousands of partially decomposed rooted trunks that found on the southeastern side of Muthupet lagoon are indicating the past, indiscriminate exploitation.

(100–150 m in width and 5–6 km in length). The density of mangroves in eastern side of Muthupet lagoon is comparatively lower than other areas. Tamil Nadu forest department has excavated several canals across the mudflat. Each main canal which enhances the water movement between sea and lagoon, has several sub canals on either side with a substantial number of mangrove seedlings. The western side is not straight a protruding land pocket has formed an islet like structure. This part of the lagoon lies near to Koraiyar river mouth with small mangrove patches.

Ontario Lacus

Ontario Lacus is a lake composed of methane, ethane and propane near the south pole of Saturn's moon Titan. Its character as a hydrocarbon lake was confirmed by observations from the Cassini spacecraft, published in the 31 July 2008 edition of Nature. Ontario Lacus has a surface area of about 15,000 square kilometers (5,800 sq mi), about 20% smaller than its terrestrial namesake, Lake Ontario in North America. In April 2012, it was announced that it may be more like a mudflat or salt pan.


Pieterburen is a village in the northeastern Netherlands, located in the municipality of Het Hogeland, Groningen.

Pieterburen is situated on the ‘Hogeland’ (high land) of northeastern Groningen. It is an area with brick Gothic churches, stately farms, and endless views over the land, all the way to the Wadden Sea.

Pieterburen is known for its Seal Rehabilitation and Research Centre, the vicarage garden Domiestoen, the old mill De Vier Winden (The Four Winds), and for mudflat hiking in the Wadden Sea. Its medieval castle, Huis ten Dyke, was torn down a century ago.

Pieterburen is the start of the Pieterpad, a long-distance hiking trail to Sint Pieter in the extreme south of the Netherlands

Saga Airport

Saga Airport (佐賀空港, Saga-kūkō) (IATA: HSG, ICAO: RJFS) is an airport in the Kawasoe area of Saga, Saga Prefecture, Japan. It also uses the unofficial name Kyushu Saga International Airport (九州佐賀国際空港, Kyūshū Saga Kokusai Kūkō).Saga Airport is located on the edge of the Ariake Sea, in what could best be described as a reclaimed mudflat, 35 minutes from JR Saga Station by bus.

Westpoint Slough

Westpoint Slough is the largest of several sloughs feeding into Redwood Creek in San Mateo County, California, United States. This slough is surrounded by extensive undisturbed marshlands including Greco Island, which forms its northern boundary. The channel of Westpoint Slough contains considerable mudflat areas; moreover, both the marshes and mudflats offer considerable habitat area for local and migratory wildlife, especially birds.

Multinational corporation Cargill currently owns 1,436 acres (2.2 sq mi) of salt ponds adjacent to part of Westpoint Slough. Cargill, in conjunction with Arizona-based DMB Associates, has proposed a highly controversial development of 32,000 people and 12,000 houses on this open space.

Pacific Shores Center sits along Westpoint Slough, as does Westpoint Harbor, which is open to the public. The Port of Redwood City, the City of Redwood City, and the Water Emergency Transit Authority are proposing to construct a commuter ferry terminal along the slough.


A windwatt is a mudflat exposed as a result of wind action on water. They occur especially in the Western Pomerania Lagoon Area National Park on Germany's Baltic Sea coast. The term is German.Unlike the Wadden Sea along Europe's North Sea coast, the shallow water zones of the Western Pomerania Lagoon Area National Park are largely unaffected by oceanic tides. When there are strong winds in a certain direction, however, water is driven out of the lagoons (the so-called bodden) into the Baltic Sea, so that several particularly shallow areas of mud become exposed and dry out. The water flows back when the wind turns again.

These windwatts are a major source of food for migrating birds in the autumn. For the Crane, which cross Western Pomeranian bodden country during migration, the windwatts are one of the most important resting areas in Western Europe.

Aquatic ecosystems
Classification systems


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