Rivers, lakes, estuaries, wetlands, streams, even the oceans can serve as catch basins for the land adjacent to them. Ground water aquifers serve the same purpose for the land above them. The actions of all the people who live within a watershed affect the quality of the waters that drain into and from it. Every watershed is unique and has a different size, shape, and drainage pattern, or system of rivers and streams. Two factors that determine the varying natural characteristics of watersheds are geology and climate.
Geology refers to the rock formations and how they change over time.
Climatic processes like wind and rain erode and shape the geology. As weathering occurs, from rain, snow, wind, or temperature changes, the land reshapes into peaks and valleys. Streams receive rainwater, and themselves act to erode and carve rocks, creating hillslopes and lowland areas. They break down large rocks into smaller pieces that can be transported as sediment. Together, sediment and organic matter from plants and animals make up the soils that form the skin of the watershed.