DDD, a chlorinated hydrocarbon pesticide, was applied three times to Clear Lake, California to kill larvae of the Clear Lake gnat, Chaborus astictopus. The pesticide biomagnified through the food web, leading to the loss of piscivorous birds (Western grebes)at the top of the food chain. This was the first time that insecticide concentration via food-web mechanisms was noted. Colorized photo plate at Clear Lake Mosquito Abatement District, Lakeport, California.