prodigal1 wrote in :

The water is clear, but is the lake healthy? No. Recently there have
been blooms of blue-green algae that are toxic for certain species of
fish.

Here in the South, particularly in Eastern NC, blooms of VERY toxic
Pfiesteria piscicida have driven boaters and fishermen crazy as their
toxins effect human memory in a terrible way. Large commercial hog farms
dumping hog sewage into rivers and streams is the root cause.

http://www.nal.usda.gov/wqic/pfiest.html

They call it "The Cell from Hell"....with good reason.