The water quality of Clear Lake — California’s largest natural freshwater lake — suffers from low-to-no-oxygen conditions that contribute to harmful algal blooms (HABs) and other issues, according to a report from the UC Davis Tahoe Environmental Research Center and the U.S. Geological Survey. Clear Lake has long suffered from environmental challenges associated with mercury contamination, high nutrient levels, low dissolved oxygen and HABs, which threaten aquatic and human health and the community’s cultural, recreational and economic activities.  The report, submitted to the Blue Ribbon Committee for the Rehabilitation of Clear Lake, outlines the primary causes of deteriorating water conditions at the 63-square-mile lake.