Solutions to the Problems...
As early as 1960, municipal officials wrestled with schemes to import Lake Washington water to make Green Lake a more pleasant place to swim. In 1991 city crews spread 181 tons of aluminum sulfate, more commonly known as alum, into the lake. Alum binds up the phosphorus and makes it unavailable to fuel the growth of the algae. The alum treatment is projected to retard the growth of the Aphanizomenon sp. for about five years, but the mud-loving common carp that thrive in the lake stirred everything up. The city has tried electrically stunning and removing the carp, which both proved inefficient; in late 2000, the department released hundreds of predatory tiger muskelunge on them, and year later, it released 777 Asian grass carp (a different fish that doesn't stir the muck) to eat the milfoil which adds to the nutrient load when it rots.
The grass carp is credited to doing "well", but not enough--the milfoil's survived them, just as it survived herbicide and mechanical mowing--a huge underwater lawnmower that used to chug around mowing the milfoil six feet under water now sits in the middle of the lake. Scuba-diving volunteers once offered to pluck out the weed, but the weather turned bad on the weekend they chose and was never taken into action.
Chemical, mechanical, and biological means have failed to control milfoil and algae, which are both accelerating the eutrophication of the lake. The Seattleites have put much effort into preserving the lake, but there needs to be a different, newer method in slowing down or stopping the aging process. The most effective of all the treatments so far was the alum treatment, but "there's a lot of community opposition to putting foreign substances in the lake." Some people around Green Lake would not mind adding chemicals to have cleaner water, but others might have different views--stated by a former city council, "If we go down the path of putting chemicals in the lake, where will it end? Right or wrong, officials have to make a better case for it."