A watershed is an area of land that gets drained by a river and its tributaries. A watershed's boundaries are defined by areas of higher elevation, such as a ridge or mountain range, from which rain and snow melt runoff flows toward a common low point. The South Platte River Watershed begins high up in the Rocky Mountains at the origin of the South Platte River, and encompasses 28,068 square miles in Colorado, of which the Denver Metro area sits squarely in the middle.
The Denver region covers about 535 square miles, all of which are in the South Platte River Watershed. The South Platte River is the main artery of the watershed, and is fed by the many creeks, lakes and minor tributaries that come down from the mountains and hills that surround Denver. Some of these tributaries include Cherry Creek, Bear Creek, and Sand Creek. The water that fills the city's lakes also eventually makes its way into the streams. In addition, drainage ditches, intermittent streams and, most critically, storm sewers, empty into the watershed.
The South Platte River Water Shed (USGS, 2004)
Even though you may live miles from the South Platte River, you are part of its watershed, and the actions you take can impact - for better or worse - the health of the river. The drainage ditch that goes through your local park, or the storm grate in the street (even the gutter in front of your house) is your personal connection to the South Platte River watershed.
This is why every individual action matters, why especially in an urban area where millions of people live and work, the cumulative actions of a watershed's residents can have such a powerful impact. Everything you do, from watering and fertilizing your lawn, to washing your car, to disposing of household hazardous materials, to walking your dog, can impact the watershed.