A watercourse is a moving body of water such as a stream, river, brook, or creek. By definition, watercourses must be flowing, but they may be natural or artificial, and they can also be seasonal, especially in areas with dry seasons which eliminate some bodies of water until the wet season arrives. A watercourse which is large and deep enough to be navigable is called a waterway; waterways can also be seasonal, reflecting fluctuations in water and sediment levels which could render a body of water temporarily unnavigable.
Watercourses are an extremely important part of the natural environment, and the study of watercourses is extensive and quite diverse. Watercourses carry runoff from glaciers, snow, and springs, providing water for animals and irrigation for plants, establishing unique habitats along the way. They can also carry sediments, provide a habitat for aquatic animals and plants, and shape the landscape as they wend their way across it.
The health of a regional watercourse is often of great importance o biologists and scientists, as unhealthy waterways can quickly make the surrounding area unhealthy. The study of watercourse health and management focuses on issues like water use, dams, erosion around watercourses, pollution, and animal studies to see which creatures call the area around the watercourse home. Fish and algae populations are often used as gauges to see how healthy a watercourse is.
A collection of watercourses which joins together at a single point to drain into an ocean or a large inland body of water is known as a watershed. All of the watercourses within a watershed are interconnected, so things which happen to one watercourse can affect the watershed as a whole. For example, if a watercourse becomes contaminated with agricultural runoff, it can carry pesticides, fertilizer, and herbicides down the watershed, polluting all of the water downstream and potentially causing significant environmental harm.
In addition to being an important part of the environment, watercourses are also important for human populations, who use watercourses to supply water to their communities, navigate, and recreate. Many humans enjoy swimming and boating on regional watercourses, and some people find it pleasant to live or work near a body of moving water, viewing the water as relaxing and pleasing to look at. Historically, human settlements are often very close to watercourses, because water is so important to human existence.