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Watershed Basics

San Juan River Watershed. Click for larger view.

A watershed is a geographic area that drains into a common body of water such as a stream, lake or river. Its boundary will more or less follow the highest ridgeline around the stream channels and meet at the bottom or lowest point of the land where the water flows out of the watershed. Much of the water in a watershed comes from precipitation and stormwater runoff.

A watershed affects the water quality in the waterbody it surrounds. Everybody lives in a watershed, so impacts to watershed health also impact human and ecological activities within the watershed. A healthy watershed supports:

  • Important hydrologic and landform processes
  • Habitat for a variety of plant and animal species
  • Healthy biological communities

Many communities and individuals rely on healthy watersheds for clean drinking water, recreation, and agriculture. Upstream activities such as mining can impact an entire watershed even if the contamination appears localized.

Watershed Monitoring

Watershed monitoring is the periodic or continuous collection of data using consistent methods. Water-quality monitoring generally includes the sampling and analysis of water and the conditions of the waterbody to evaluate its physical, chemical, and biological characteristics. Watershed monitoring is a comprehensive approach to data collection that evaluates the condition of the water resource while also providing valuable watershed information to help establish cause-and-effect relationships. Watershed monitoring data can be used to determine the source(s) of impairment, provide input for management tools such as models, and support scientifically-based decisions for preserving or improving the quality of a water resource.

The San Juan Watershed

The San Juan River is approximately 355 miles long and originates in the San Juan Mountains in southwestern Colorado. It flows westerly into New Mexico and is detained in the Navajo Reservoir. The river continues into southern Utah and ultimately terminates in Lake Powell in Utah. Lake Powell lies on the Colorado River, along the Utah-Arizona border. At 186 miles long and with 1,960 miles of shoreline when full, the lake is the second largest manmade reservoir in the country. The 126-mile long Animas River originates in the mountain peaks northeast of Silverton, Colorado, and flows southward and into the San Juan River in Farmington, New Mexico.

Water resources in the San Juan watershed are essential for recreational, agricultural, cultural, ecological, and residential uses. Potential contamination sources within the watershed include historic mining activities in the Bonita Peak Mining District of Colorado and naturally occurring mineralization in the area.