Blue-Green Algae, or cyanobacteria, are extremely resistant to conventional chemical control methods. The mat-forming species often appear greyish-green or brownish-blue in color. Mucus covering prevents environmental pressures and chemicals from damaging the cells.
Cyanobacteria can acquire nitrogen directly from the air if dissolved supplies run low. They can also store phosphorus for later use, enabling them to out compete other plants.
Disturbances from boating and spraying often release more patties from the bottom. Changes in weather and water chemistry tend to help most in blue-green reduction. Specialized products are available at additional cost but control cannot be guaranteed.