Along the Georgia coast, our estuarine habitats include the coastal rivers, salt marshes and tidal marsh creeks. Seawater from the ocean and freshwater, draining from land, mix together in estuaries. It is to be expected to find a range of salt concentrations throughout an estuary. The salinity of the water affects the organisms living in it, and some species are more tolerant to a wider range of salinity than are others. Other species, however, have narrower tolerance limits and are usually found in only certain portions of an estuary.
Salinity refers to the concentration of dissolved salts in seawater.
The salinity of average ocean water is 35 ppt, although along Georgia beaches the salinity is usually closer to 30 ppt, due to the input of fresh water from our rivers. As you move from the ocean into an estuary, the salinity generally decreases. Because saltier water is denser than fresher water, it is not unusual to find slightly saltier water near the bottom with less salty water near the surface. In fact, this saltier, denser water actually moves upstream along the bottom of an estuary. In Savannah, right now, there is controversy regarding the planned deepening of the Savannah River harbor and channel because it is predicted that deepening would allow more salt water to flow further upriver.