Tidal Freshwater Marsh


Tidal freshwater occurs when the lunar tides from the ocean meet out-flowing freshwater moving through rivers and streams from their headwaters. The dense saltwater from the ocean pushes a wedge under the river’s freshwater, causing it to rise (as far as 45 miles upriver in the Savannah River) and flood surrounding marshes. At low tide, the saltwater wedge retreats, and the river level falls, exposing the marsh floor.  

The high plant and structural diversity of these wetlands provide excellent resting, feeding, and nesting habitat for many bird species, including neotropical migrants, wintering waterfowl, and resident wading birds. Many fur-bearing mammals like mink, beaver, and river otter also thrive in this unique environment. 

Decades of development along the east coast of the United States has resulted in much of this valuable wildlife habitat being destroyed or replaced by salt marsh, which studies have shown to be far less biologically diverse. Savannah National Wildlife Refuge currently protects a substantial portion of the tidal freshwater marsh that remains.