There is a salt wedge effect as heavier salt water moves upriver along the bottom during flooding tides. The salt wedge can move 15 miles upriver during periods of low freshwater flow. Differences between the surface and bottom salinities can be more than 20 ppt. Surface salinities in the bay range from 0 to 10ppt with ranges from 29 to 32 ppt at the ocean entrance. Winter temperatures are highly variable but generally mild.
Ice occasionally forms on high marsh pools, but snow is a rare event.
Rainfall is about 45 inches per year. Winyah Bay is a drowned river basin receiving water from an extensive watershed associated with the Black, Pee Dee, Waccamaw, and Sampit rivers. This web site is maintained by the Baruch Institute .