Forward Thrust, a 1968 clean water initiative along with some other things. Lk WA was so polluted because many of the urban sewer outfalls dumped untreated sewage directly into the lake. OK, maybe there was primary, but no secondary treatment. The lake was too dirty to allow people to swim in it, for example. Seattle didn't want to wait around for the Clean Water Act to force them into action. For a majority of people, producing the maximum number of sockeye smolts wasn't the most important attribute of Lake Washington.