If your having algal blooms try to get rid of the phosphorus (P) in your lawn fertilizer. The P is what cause most of the algal blooms. Many people try to blame it on the farmers and spreading manure. Yes, this does contribute to the problem but all the people fertilizing their lawns far out weighs what the farmers are doing. Try to find a lawn fertilizer with no P in it, it is a little harder to find put much better for the environment. You really don't need that much P and you probably have enough in the soil naturally.