The Lake Washington Story
Water quality is greatly influenced by human activities, but other seemingly subtle biological activities also have great significance. Lake Washington is an interesting example of how human influences and biological processes can alter water quality. The late Dr. W.T. Edmondson, former professor of zoology (external link) at the University of Washington, (external link) studied the biology and chemistry of Lake Washington for many decades. The 1955 discovery of the cyanobacteria Oscillatoria rubescens (formerly called a blue-green alga) in the lake, by oceanographer George Anderson, led to further research and predictions that nutrient conditions would soon be stimulating nuisance algal conditions, as had been documented in Lake Zurich in Switzerland.
Unlike algae, which assails the eyes and the nose, some factors of water quality are invisible and can be measured only in the laboratory. Dr. Edmondson's studies implicated phosphorus from sewage as being the element from treatment-plant effluent that fertilized algae in Lake Washington. Phosphorus was found in concentrations of 70 parts per billion in the 1960s. That was enough to feed the significant growth of algae that darkened the water and washed ashore to rot and smell. This finding had major implications for industry, and great political discussion resulted. King County's history of community involvement continues to this day.
Metro was established in 1958 and entrusted with the task of diverting sewage from the lake. Between 1963 and 1968, more than 100 miles of large trunk lines and interceptors were installed to carry sewage to treatment plants built at West Point and Renton. Treated effluent ended up in Puget Sound, where currents and tidal action diluted it. At the time, the $140 million dollar campaign was considered the most costly pollution control effort in the country. Go here to read more about how King County protects water quality in the Puget Sound region.
Just as Dr. Edmondson had predicted, completing these major facilities brought dramatic results. Effluent, which was at one time entering Lake Washington at the rate of 20 million gallons per day, was reduced to zero discharge in February 1968. After the last lakeshore treatment plant was closed, the concentration of phosphorus dropped quickly to about 16 parts per billion, a level maintained into the 1990s and beyond.The lake's transparency, as low as 30 inches in 1964, reached 10 feet in 1968. Water quality would continue to improve: in later years the transparency would reach depths of 17 to 20 feet, with a maximum depth of nearly 25 feet in 1993.
Improvements to transparency after 1976 increased beyond what could be accounted for by the measured amount of phosphorus. This increase came about with changes in the composition and relative abundance of the algae, zooplankton, and fish.
During Lake Washingtons period of eutrophication in the 1960s, the cyanobacteria Oscillatoria rubescens was a prominent nuisance, forming thick masses near the surface of the water. This species is relatively long and filamentous, generally unsuitable food for grazing zooplankton. Oscillatoria has inhibitory effects on other algae through the physical impact of shading and through biochemical means. Since phosphorus is a necessary nutrient for Oscillatoria, it was able to thrive in the phosphate-rich lake water. With the sewage diversion from the lake and resulting decrease in available phosphorus, conditions were no longer ideal for Oscillatoria, and it diminished entirely in 1976.