The problem was blamed on rain water runoff from the mostly urban area located upstream on Onion and Williamson Creeks. The run off dumped animal waste, oils, dirt and debris into the creeks. Another contributor was the Williamson Creek Wastewater Treatment Plant. The plant would occasionally dump effluent in various stages of treatment into Williamson Creek if there was equipment failure. By 1982, the plant was overloaded by the rapid growth of the city and regularly discharged effluent into the creek, not all of which met state standards for discharge.