Fresh and Salt Water Marshes
Swallows in Marsh


Marshes are a type of wetland with flora and fauna that adapt to being flooded with water and to living in saturated soils. Approximately 60% of the United States’ marshes are found near shorelines of the northeast Gulf of Mexico. Florida alone is home to about 500,000 acres of salt marsh. While about 70% of Florida’s salt marshes occur along the state’s northern coastline, South Florida boasts large expanses of freshwater marsh including the more than 1.5 million acres of the Everglades. These productive marsh habitats comprise much of Ten Thousand Islands National Wildlife Refuge and its surrounding areas. Read more to learn why the marshes of this refuge are so special! 

Freshwater Marsh

Freshwater marshes are habitats intermittently or persistently flooded with water from non-tidal systems. As the name suggests, the water in these marshes is not salty or brackish. The water in freshwater marshes may arise from groundwater, streams, surface runoff, or precipitation. 

Freshwater marshes do not have peat soils like those found in bogs or fens. Rather, these mineral rich soils are of sand, silt, and clay. 

Marshes are typically defined by a lack of woody vegetation. Rather than trees, freshwater marshes contain grasses and sedges that are adapted to live in saturated and changing conditions. Cattails, bulrushes, saw grass, and maidencane are some of the most common species of vegetation found throughout South Florida’s freshwater marshes. Other types of marsh vegetation may be submerged or float on the water’s surface such as bladderworts and water lilies. 

The dry, winter season from December through April is the best time to view wildlife in freshwater marsh habitat. Species typically found in this habitat type include otters, mink, raccoons, and various reptiles including the alligator. An impressive variety of wading and migratory birds can be seen in Florida’s freshwater marsh throughout the year. 

Salt Marsh
Salt marshes are found at the border of saltwater bodies, like the Gulf of Mexico in Southwest Florida. This type of habitat is part of the tidal system where fluctuating water levels flood the marsh during high tide.
The soil of salt marshes is similar to that found in freshwater marshes. This soil consists of sand and silt that is highly organic. The organic matter component of soil is made up of organisms in various stages of decomposition. 

Salt marshes are subject to high wave action, periodic flooding, storm erosion, and salt. Vegetation that grows in salt marshes must be well adapted to survive these conditions. Cordgrasses, rushes, and sedges are the types of grasslike plants that make up about 90% of vegetation found in Florida’s salt marshes. These plants and the algae growing within the water stabilize the marsh as well as provide food and shelter for diverse birds, fish, and mammals that rely upon this habitat. 

Like vegetation, wildlife that inhabits the salt marsh must also be well adapted to thrive in saline and saturated conditions. As you’ll read in the “Importance” section of this habitat profile, nutrient rich salt marshes are critical habitat for a diversity of well-adapted species. Salt marshes along the Gulf coast are famed for abundant crustacean, fish, and bird species. Alligators are the primary reptile found within salt marshes. Several species of mammal also call the salt marsh home. These may include raccoons, mice, rabbits, and feeding dolphins.

It is estimated that 10% of Florida’s salt marshes have been lost. Some urban coastal areas have lost a great deal more, like the Indian River Lagoon which has experienced about an 85% reduction in its salt marsh.

Both salt and freshwater marshes are threatened by altered water cycles that arise from human development like channels and impoundments. Filling for development and pollution are other human-induced threats to marshes.

Climate change and sea level rise also alter marsh habitat.

Development restrictions, mitigation, and restoration like the Comprehensive Everglades Restoration Plan ( all support marsh habitat.

Yet, the population of Florida’s coast continues to grow and marshes remain sensitive to pressures of development. Understanding the various threats to marshes can also help us recognize why places like Ten Thousand Islands National Wildlife Refuge are so valuable for our water resources, plant and animal communities, and the people who rely upon them.

Marshes are home to a diversity of organisms, both innately important to naturally balanced ecosystems and human needs. 

High levels of nutrients and the consequent rapid growth of marsh vegetation allows these habitats to be some of the most productive in the world. 

Marshes contain intricate species interactions that contribute to ecosystem health and productive food webs. For example, crustaceans like the fiddler crab excavate marsh soils to create the burrows in which they live. This excavation aerates the soil and helps grassy vegetation to thrive in the marsh. Another example can be found among plants and algae that produce large amounts of organic material in this fertile habitat. In turn, herbivores and detritivores consume the organic material.

With calm waters, few predators, and abundant food sources, salt marshes provide essential nursery habitat for many ocean species. It is estimated that salt marshes along the Gulf Coast are nurseries for 70% of Florida’s recreational and commercial fishes, crustaceans, and gastropods. Even non-aquatic organisms benefit from the marsh nursery, such as birds who use this habitat as nesting sites. 

Marshes also naturally prevent damage to coastlines. These habitats stabilize shorelines, filter pollutants, absorb excess nutrients from runoff, and mitigate flood damage.


University of Florida. 2012. Freshwater Marshes. IFAS Extension. Retrieved from:

University of Florida. 2012. Gulf Coast Salt Marshes. IFAS Extension. Retrieved from:

Sweat, L.H. 2009. Salt Marsh Habitats. Smithsonian Marine Station at Fort Pierce. Retrieved from:

Stout, J.P. 1984. The ecology of irregularly flooded salt marshes of the north-eastern Gulf of Mexico: A community profile. U.S. Fish and Wildlife Services. Biol. Rep. 85(7.1) 98pp.

United States Environmental Protection Agency (USEPA). 2012. Marshes. Water. Retrieved from:

Facts About Marshes

Covering 3,861 square miles (10,000 square kilometers), the Florida Everglades is the largest freshwater marsh system in the United States 

The rotten egg smell of the salt marsh is caused by anaerobic bacteria and the decomposition of abundant organic material 

High concentrations of mosquitoes caused salt marshes to be one of the last habitat-types to be impacted by Florida’s rapid population growth in the 1930s. Pesticide development and water impoundment measures ultimately overcame the mosquito problem in marshes and led to an increase in their human habitation