The most recent National Lakes Assessment conducted by the Environmental Protection Agency shows there has been no net change in the nation’s lake water quality since 1972. With the enactment of the Clean Water Act and the investment of billions of dollars, how can this be?
Early on, many lakes improved followed the treatment or diversion of sewage effluent. Lake Minnetonka is an example. However, since the early 1980s, when sewage effluent was largely under control, most remaining lakes have not changed and about a quarter of the lakes have declined in quality.
Source: Lake Manager’s Notebook by Dick Osgood, CLM: Lessons Learned