A Biologist is good. A Limnologist would be better.
Here's a "budding Limnologist" searching for algae.
I searched Google for an algae that cleans, and turned up nothing. I suspect the algae you saw could have been thick enough to rob native vegetation of sunlight.
I'd agree that the algae started appearing along with the oversized boats that started to appear about the same time. Their wakes dragged Phosphorus from shorelines into the shallows.
But it was about 1971 that the Legislature declared the lake's quality to be less than its former "
drinking water quality".
Member
winterh would be interested.
.