Covering approximately 400 square miles, Tampa Bay is Florida’s largest open-water estuary. The drainage basin for Tampa Bay consists of over 2,200 square-miles of land from Hillsborough, Manatee, Pasco, Pinellas, Polk and Sarasota Counties. About 80% of the 525 billion gallons of freshwater that annually flows into Tampa Bay does so from the Alafia, Hillsborough, Little Manatee, and Manatee Rivers. Two rivers, the Hillsborough and Little Manatee, are designated by the Florida Department of Environmental Protection as Outstanding Florida Waters, a category of waterbody worthy of special protection because of their natural attributes. In 1990, Congress designated Tampa Bay an “estuary of national significance” adding the waters to the US Environmental Protection Agency’s non-regulatory National Estuary Program and laying the foundation to establish the Tampa Bay Estuary Program.