Water usually runs into ditches, streams, marshes or lakes, and the land from which the water drains to any of these collection points is called a watershed. Watersheds can be a few acres or as large as several thousand acres. Large watersheds are actually made up of many smaller ones. Everyone lives in a watershed. Healthy, managed forests contribute to the quality of water produced in a watershed.
Trees take up great amounts of water through their roots and evaporate it into the air.
This usage and retention of water reduces flooding. Forest soils act as high reservoirs for ground water, releasing it slowly, even during periods of low rainfall, The forest floor acts as a natural sponge because of the large soil pore spaces, thus keeping soils or contaminants from entering streams. When soil filled water reaches the forest, water is quickly absorbed and the soil particles are deposited there. This effective infiltration system reduces overland flow leaving little chance of erosion. Maryland has six major watersheds.