If you know how much water enters a lake and how much leaves, what can you figure out about the lake's water level changing?

If you know how much water enters a lake and how much leaves, you can figure out the net change in the lake's total water volume and, consequently, the direction and magnitude of its water level change. Water entering a lake, referred to as total inflow, encompasses all water sources that contribute to the lake's volume, such as rivers and streams flowing in, direct precipitation (rain or snow) falling onto the lake's surface, and groundwater seeping into the lake. Water leaving a lake, referred to as total outflow, encompasses all ways water exits the lake, such as rivers and streams flowing out, evaporation from its surface (where liquid water turns into water vapor), and groundwater seeping out from the lake. The water balance principle states that the change in a lake's water storage, or total volume, over a specific period is equal to the total water entering minus the total water leaving during that same period. If the total water entering is greater than the total water leaving, the lake experiences a net gain in water, which causes its total volume to increase and its water level to rise. Conversely, if the total water entering is less than the total water leaving, the lake experiences a net loss of water, which causes its total volume to decrease and its water level to drop. If the total water entering is exactly equal to the total water leaving, there is no net change in the lake's total water volume, and its water level remains stable. The lake's water level is a direct measure of its contained volume; thus, any change in the lake's volume directly translates into a corresponding change in its water level. The specific magnitude of this water level change also depends on the lake's surface area: for a given change in volume, a larger surface area will result in a smaller change in water level, while a smaller surface area will result in a larger change.