Once known for its therapeutic qualities, Medical Lake in Washington fell into eutrophication. However, a targeted alum treatment in 1977 greatly mitigated phosphorus levels, effectively curbing algal growth. This intervention not only clarified the water but also revitalized the lake’s ecosystem, leading to the return of larger zooplankton and the successful reintroduction of trout. Medical Lake now serves as a model of effective lake restoration efforts across the country.