Water from Lake Okeechobee and The Big Cypress eventually flows to the ocean. At a transitional zone where fresh water meets salt water, mangrove trees thrive, adapted as they are to both kinds of water. This brackish mixture of water and mangrove systems, crisscrossed by hundreds of tidal creeks, harbors a very productive ecosystem. The depth of these zones is dependent on how much water flows from the Everglades. In the wet season, fresh water pours into Florida Bay and sawgrass appears near the coastline. In dryer years, salt water creeps inland to the coastal prairie, an ecosystem that buffers the freshwater marshes by absorbing sea water. Mangrove trees grow in fresh water ecosystems when the salt water flows far enough inland.[64] The Everglades have the most extensive contiguous system of mangroves in the world.[65] The mangrove forests of the Ten Thousand Islands cover almost 200,000 acres (810 km2).[66]