A summer heat wave is blazing away in Southern California but state officials are warning against taking a cool dip in Pyramid Lake. The Department of Water Resources said this week that a cyanobacteria algal bloom first detected in June is continuing at the lake just off Interstate 5 in northwestern Los Angeles County. Recent sampling for toxins showed levels high enough to keep no-swimming signs posted on the lake's beaches. The department says sunlight, warm temperatures, nutrients in the water and calm conditions contribute to algal blooms. Picnicking and hiking near the water is safe, but the water should not be used for cooking, and boaters should avoid running over mats of algae to prevent accidental ingestion of spray.