Tide Pools

Mud Beaches

Follow a stream or river to Puget Sound, and you'll often find a mud beach or mudflat. Look for wide open tideflats and meandering tidal channels. Two examples of mud beaches are found at Mud Bay in Thurston County and Fidalgo Bay in Skagit County. Mud beaches are only found in protected areas because high waves and currents wash mud away.  

Packing It In

What is a mud beach made of? A highly complex goo loaded with biological food. More invertebrates are packed into the high intertidal zone of mud beaches than any other type of beach. That means lots of food for shorebirds and fish - which feed on invertebrates (clams, shrimp, worms, and microscopic organisms).

Mud shrimp

What Makes Mud Beaches Smell?

You could call it the scent of life. The smell comes from gas produced by anaerobic bacteria who get chemical energy from sulfur compounds, much in the same way that plants get energy from sunlight. These anaerobic bacteria contribute to the production of mudflats, and in turn nourish large numbers of animals.

Mud Beach: Habitat Zones

  • High Intertidal Zone
    High intertidal areas are exposed for long periods of time at low tide, giving shorebirds ample opportunity to feed. During winter, when the mean tide levels are higher, the birds become more dependent on the high intertidal zone on mudflats. Waterfowl are also abundant. Green-winged teal, canvasbacks, and ruddy ducks can commonly be seen feeding in these areas.
  • Lower Intertidal Zone
    Large numbers and varieties of fish feed along mud beaches especially if eelgrass is present in lower intertidal and shallow subtidal areas. Species include: juvenile English sole, starry flounder, three-spine stickleback, shiner perch, sharpnose sculpin, surf smelt, and Pacific Herring. In addition, tidal channels provide important feeding areas for salmon.

    Packing In Pollutants

    Typically, there is not much wave action or flushing of mud beaches. As a result, toxins can build up. Pollutants discharged into the water in small but constant quantities can add up to high levels. The buildup of coliform bacteria can make shellfish, particularly oysters, unsafe to eat.

    Related Links

    Beaches, US EPA. Find information on beach basics, beach health, and technical resources. 

    The Beach and Your Coastal Watershed, US EPA Fact Sheet (1998). Beaches and their function within a coastal watershed. Impacts on beaches and EPA's programs to protect beaches. 

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