Answer:
The cleaning up of Lake Washington didn't occur overnight. It started with the process of providing scientific information to the public and the public decided to take action.
The action was persistent and the results yielded took a long while to materialize properly.
Upon receipt of the information from scientists that a particular bacteria was responsible for damaging the ecology of the water body, the public resorted to conveying all effluents to a treatment plant rather than dump same in to the Lake.
Cheers!