The consistent Everglades flooding is fed by the extensive Kissimmee, Caloosahatchee, Miami, Myakka, and Peace Rivers in central Florida. The Kissimmee River is a broad floodplain that empties directly into Lake Okeechobee, which at 730 square miles (1,900 km2) with an average depth of 9 feet (2.7 m), is a vast but shallow lake.[22] Soil deposits in the Everglades basin indicate that peat is deposited where the land is flooded consistently throughout the year. Calcium deposits are left behind when flooding is shorter. The deposits occur in areas where water rises and falls depending on rainfall, as opposed to water being stored in the rock from one year to the next. Calcium deposits are present where more limestone is exposed.[23]