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 with 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. Project implementers have flexibility to prioritize the most cost-effective projects, often focussing on pollutant source control practices – like street sweeping – instead of expensive capital development projects. 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.
Urban implementers have worked through challenges to complete their first registrations of pollutant controls in the Lake Clarity Crediting Program. The program tools have enabled implementers to report quantitative load reductions, and associated Lake Clarity Credits, linking management to actual water quality benefits in a way that previously wasn’t possible. Results show permittees exceeding the first five-year milestone, a 10% fine sediment particle reduction. Basinwide, Urban implementers achieved 118% of the total credits targeted, with nearly all surpassing their individual credit targets.