Salt marshes, tidal creeks and mangroves - A large salt marsh cuts a wide swatch across the northern section of Rattlesnake Island from the Matanzas River to the Intracoastal Waterway. A number of smaller salt marshes occupy the center of Rattlesnake Island. Tidal creeks meander north out of those smaller marshes to join larger creeks that drain the large marsh into the Matanzas River and Intracoastal Waterway. Another large salt marsh and tidal creek complex lies outside the north boundary of Fort Matanzas National Monument on Anastasia Island. A small strip of salt marsh runs south along the east side of the Matanzas River to the Fort Matanzas National Monument Visitor Center.
Salt marshes are salt tolerant grasslands lying between the high and low tides.
The tidal flow through the larger creeks fills them with sea water, but the upper reaches of the tidal creeks and pools in the smaller marshes are hypersaline from evaporation. Most salt marsh animals are found on the surface, in the vegetation, or in the tidal creeks. Diamondback terrapins range through the saltwater habitats of Fort Matanzas National Monument, including the tidal creeks. Eastern glass lizards , corn snakes , pine woods snakes , and six-lined racerunners are found along the edges of the salt marsh. The trunks of the trees are more erect and there is no salt and wind sculpting of the canopy.