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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Wetlands of the Pacific Southwest

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Mudflats

Tidal mudflats at Morro Bay, California

Tidal mudflats at Morro Bay, California

Mudflats are unvegetated areas of fine-grained sediment (mud) that are sometimes flooded. They are found both in tidal areas and in freshwater lake and river systems. Mudflats are extremely productive areas for invertebrates (worms, clams and other shellfish). In tidal areas they provide rich foraging grounds for shorebirds (at low tides) and other birds and fish (at high tides). Mudflats often support recreational and commercial fisheries, such as clam and oysterbeds.

Shucking oysters from tidal mudflats

Oysters can be grown in tidal mudflats and shallows.

Mudflats are particularly extensive in the San Francisco Bay and estuary where about 30,000 acres still exist. Smaller mudflats can also be found in bays and estuaries throughout California and, to a lesser extent, some Pacific islands. Because mudflats are typically shallow areas near the shore, they are at risk from dredging (for navigation) or filling (for levees or land development), sewage, and polluted runoff from adjacent lands.

Like coral reefs and vegetated shallows, mudflats are “special aquatic sites” protected under the Clean Water Act.

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