A color satellite image of the lower third of the Florida peninsula with labels superimposed over major landscapes before human alterations: directly to the south of Lake Okeechobee is a thin custard apple and cypress swamp, a much larger cypress swamp borders the lake to the east, and a major section of western pine flatwoods borders it to the west. Massive sawgrass plains are formed to the south of the custard apple swamps, which eventually merge into ridge and slough formations that narrow into the Shark River that flow into the Gulf of Mexico. Where the Shark River forms the area is lined with marl marshes, and the Big Cypress Swamp is located between the ridge and slough formations and the Gulf of Mexico. To the east the Atlantic Coastal Ridge rises slightly above the Everglades, which is where the major population centers are located