St. Johns County is a county in the northeastern part of the U.S. state of Florida. As of the 2020 United States census, its population was 273,425. The county seat and most populous incorporated city is St. Augustine, although the nearby community, St. Johns, has a higher population.
In St. Johns County, Florida, key bodies of salt and brackish water include Matanzas Bay, Matanzas River, and Salt Run. Lake George, also known as Lake Welaka, is a broad, shallow brackish lake on the St. Johns River. The St. Johns River itself is an estuary, meaning it's a mix of saltwater and freshwater, and this area is also considered part of the brackish water system. Additionally, there are various creeks, tidal marshes, and other smaller waterways that contribute to the brackish water environment in the area.
