Nutrients in stream water provide essential food for plants and animals. They occur naturally due to processes such as weathering and erosion, breakdown of organic material, and atmospheric deposition. Nutrients in surface waters can also result from human activities such as fertilizer application, runoff from agricultural and urban areas, effluent from wastewater treatment, seepage from septic tanks, detergent, animal waste, and fuel combustion. In the last decade, concerns about cyanobacteria and associated cyanotoxins have been expressed by stakeholders in the Yampa River Basin as algal blooms have been reported in local lakes and reservoirs, so this indicator will remain important to evaluate for the Scorecard.