When a bloom goes toxic, generally it cannot be treated and the remedy is to wait until the bloom dies off. While weeds and alga do not ordinarily bloom and thrive at the same time, it is not always so. When the nutrients are rich and the sunshine is plentiful you can have both weeds and toxic alga. Other Conditions That Have Occurred In 1992, when treatment was prohibited, there was a large snail die-off and the shore was covered with millions of dead snails. Fish can die from suffocation or alga toxins when weed and alga conditions are not kept in reasonable balance.
Weeds are necessary for fish habitat and alga feed the creatures that feed the fish.
Too much of any of the conditions that are caused by excessive nutrients in the lake can kill fish, wildlife and humans. This is a duck that did not survive the conditions in the lake. However most of the ducks clear paths through the weeds and survive. This is a picture of a young man in a wet suit that ducked down to the bottom and came back up. This was only one time.