Book 30, Question 18
How does water get into and out of a lake?
Water comes in from rain, rivers, streams, melting snow, and underground springs.
It leaves through an outflowing river, by evaporating into the air, and by seeping into the ground. A lake stays full when the water coming in balances the water going out. Some lakes have no outlet, so water leaves only by evaporation, which can make them salty over time.