Explain how each person and group played a crucial role in the cleanup of lake washington

Lake Washington is located in Washington state USA and has been 'saved' from pollution by the efforts of some groups. During the 1950s sewage treatment plants operating near the banks of the lake released effluent in the lake environs. This lead to the proliferation of some species of algae that caused the water to become cloudy and also increased the level of phosphorus in the water. Citizens living in the lake environs pressured authorities to take action and this lead to the government to set up a system where the sewage is diverted from the lake and to a zone where it can be safely diluted with sea water. 

What are the choices?