Much of the remaining water seeps or soaks into the ground water and moves underground toward lakes and rivers. Water that runs off the land surface also enters rivers and lakes. Lake levels vary from season to season and year to year. Precipitation is the principal cause of lake level fluctuation. However, the lag between precipitation and lake level change varies from days to years, depending on the lake.
Dams can modify some fluctuations, but varying lake levels are normal.
Water is most dense at 39 degrees Fahrenheit. Above and below that temperature, water expands and becomes less dense. Many lakes stratify in winter because ice covers the lake surface. Lakes in areas with milder winters do not stratify during the winter. Plant material either decays or sinks to the bottom and accumulates in this stagnant layer.