Long Lake, an impoundment of the Spokane River, was eutrophic prior to 1978. Extensive hypolimnetic anoxia, excessive summer algal growth and limited water clarity existed as a result of nutrient loading from the City of Spokane's primary sewage treatment plant. Advanced wastewater treatment (Am) began in the fall of 1977 with a process for 85 percent phosphorus removal. Investigations during post-AWT years (1978–1981) have shown significant reductions in phosphorus loading with corresponding declines in chlorophylla, phytoplankton biovolume, primary productivity and increased water clarity to levels characteristic of mesotrophy. Hokever, anoxia has continued to exist, although the degree of anoxia has been considerably less.