Most lakes are dynamic systems primarily fed by surface water inflows such as rivers, streams, and creeks that carry runoff from higher elevations. However, the sources of a lake's water can be much more complex than just visible rivers. Many lakes are replenished by underground springs and groundwater seepage, which can provide a consistent supply even during dry seasons. Additionally, direct precipitation (rain and snow) and surface runoff from the surrounding watershed play significant roles. In some unique cases, such as volcanic crater lakes, the water may come almost exclusively from rainfall and snowmelt with no permanent inflow stream at all. Conversely, endorheic lakes are "terminal" systems that receive inflow but have no surface outflow, losing water only through evaporation or underground seepage, which often leads to high salinity over time.