The world renowned water clarity of Lake Tahoe, which once averaged 100 feet in the 1960s, was steadily deteriorating. In 1997 measurements indicated Lake Tahoe’s clarity was only 64 feet. As a result, Lake Tahoe was listed as an impaired water body under section 303d of the Clean Water Act and water quality regulators in California and Nevada were charged addressing the problem. They knew they had to reduce pollutant loading to the lake, but how?
Environmental Incentives, in partnership with the Water Board in California and Nevada Division of Environmental Protection, developed the Lake Clarity Crediting Program. The program, formally adopted in 2011, measures the total amount of key pollutants entering the lake from urban stormwater and sets load reduction targets that each city, county and highway maintenance agency must achieve. The targets, “Lake Clarity Credits,” can be traded among jurisdictions to meet regulatory requirements. Each Lake Clarity Credit quantifies the major pollutants responsible for Lake Tahoe’s clarity loss: fine sediment, phosphorus and nitrogen. Ultimately, implementation of the Lake Clarity Crediting Program is expected to restore Lake Tahoe’s unique clarity so that people may once again see to depths of nearly 100 feet.
Though it is too early in Crediting Program implementation to analyze the relationship between lake clarity and pollutant load reductions, regulators are encouraged by lake clarity measurements that show a long trend of stabilization. Lake clarity has averaged around 70 feet for the past ten years. Existing estimates indicate that the first five year milestone, pollutant load reductions of 10 percent from 2004 levels, will be met, or even exceeded, by 2016. In addition, the Lake Clarity Crediting Program has enabled project implementers to prioritize the most cost-effective projects, electing to focus on pollutant source control practices – like street sweeping – instead of expensive capital development projects.