Water Quality

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Whether it is used for drinking, recreation, producing agricultural products (such as crops, timber, and livestock), or as habitat for fish, frogs and other creatures, water is a major export from the Sierra region. The ability to use and export high quality water, therefore, is critical to the long-term health and prosperity of the Sierra Nevada’s environment and economy.

The Sierra Nevada is directly responsible for more than 60 percent of California’s developed water supply. Nevada’s Carson Valley is similarly dependent on the Sierra. Thirteen of the Sierra’s 24 major watersheds supply water to California’s Central Valley Project, which irrigates three million acres of farmland in the Central Valley. The State Water Project built primarily on two Sierra rivers – the Feather and Kern – supplies irrigation and drinking water to nearly two-thirds of California’s population. In Nevada, the entire metro region of Reno, Carson City, Minden and Gardnerville rely entirely on Sierra water from the Truckee, Carson, and Walker rivers.

Water quality in the Sierra is directly related to the mix of land uses and management practices found in the region, as well as natural events, vegetation condition, climate, and geological underpinnings. The Changing California: Forest and Range 2003 Assessment report and many other studies identify working landscape practices along with development, recreation and other uses, as key human-induced factors in watershed health and, specifically, water quality. Working landscapes were identified for a variety of reasons such as exposing soil to erosion due to vegetation removal; introduction of contaminants like sediment, nitrogen, mercury, automotive oils, and pesticide residue into the waterways, and modification of water courses. While there is general agreement on the link between land management practices and water quality, opinions differ when it comes to how to measure, monitor, or evaluate actual impacts and determine rules, guidelines, or mitigations to lessen the impacts.

California’s State Water Quality Control Board (SWQCB) and its regional boards (RWQCB) set and enforce water quality standards for California’s waterways. Click here for a statewide map of the RWQCBs) Every two years the RWQCBs identify waterbodies (lakes, streams, rivers) in their jurisdictions that failed to meet the standards set for various beneficial uses of that water. According to the Lahontan RWQCB Basin Plan, beneficial uses can include any combination of the following: municipal, agricultural supply, industrial service supply, ground water recharge, freshwater replenishment, navigation, power generation, water contact recreation, non-contact water recreation, commercial and sport fishing, cold freshwater habitat, wildlife habitat, preservation of biological habitats of special significance, rare/threatened/endangered species, migration of aquatic organisms, spawning/ reproduction/development, water quality enhancement, or flood peak attenuation/flood water storage.

These water bodies are then listed by the U.S. Environmental Protection Agency as “impaired” under Section 303(d) of the Clean Water Act. In the Sierra Nevada, 11 of the 24 major watersheds have at least one river, lake or reservoir listed as impaired equating to a total of 535 impaired river miles and 252,044 impaired acres of reservoirs or lakes. Most of California’s Sierra Nevada falls within the jurisdiction of two regional water quality boards: Lahontan and Central Valley. Complete lists of 303(d) impaired waterbodies with mileage, acres, stressor/pollutant and source information, can be accessed for the Lahontan Regional Water Quality Board and the Central Valley Regional Water Quality Board. The Nevada Division of Environmental Protection’s Bureau of Water Quality Planning maintains completes lists of 303(d) impaired waterbodies in Nevada.

Download data 303(d) impaired waters for Nevada’s portion of the SOSA region

When a waterbody is listed as impaired, the RWQCB is required to develop a Total Maximum Daily Load (TMDL) for that waterbody. The TMDL identifies the amount of certain pollutants that can enter the waterbody over time without negatively affecting the beneficial uses of the water. Once those levels are set, the RWQCBs adopt implementation plans to reduce the pollutants and stressors that caused the listing. The intent is to bring them to levels within the allowable TMDL limits.

Working landscape practices can play a major role in water quality degradation within different parts of the SOSA region. In the Lahontan RWQCB region, which covers the East Side and portions of the Northern and Tahoe SOSA regions, silvicultural and rangeland grazing practices are factors in roughly 75% of the river and stream miles listed as impaired.