Great Salt Lake receives water from four main rivers and numerous small streams (66 percent), direct precipitation into the lake (31 percent), and from ground water (3 percent). The total average annual inflow to the lake is about 2.9 million acre feet of water. The main rivers entering the lake are the Bear River from the north, the Weber and Ogden Rivers from the east, and the Jordan River from the south. The drainage basin of the lake covers an area of about 21,500 square miles. The Great Salt Lake is a terminal lake because it has no surface outlet (rivers flowing from it). Water is lost from the lake mostly through evaporation. Evaporation rates are highest during the hot summer months and lowest during the winter. An average of about 2.9 million acre feet of water evaporates from the lake annually. When inflow equals evaporation, the level of the lake remains constant. If inflow is greater or less than evaporation, the level of the lake will rise or fall, respectively.