Toxic Algae on Grand Lake in St. Mary's OH09/13/2010Grand Lake in St. Mary's, Ohio has been plagued with the growth of a toxic blue-green algae. There are many types of algae that are harmless to the environment and people around it but this specific type of algae can affect the nervous system and the liver. Recreational activities have been virtually halted. This restriction could affect the local economy and all of the property owners. Algae grows and thrives when there is an excess of phosphorous in the water. This excess can be from many different variables...like fertilizer run off, decaying vegetation, and all other organic waste. One of the best ways to neutralize some of these naturally occurring nutrients is to introduce high levels of "good bacteria". Bacteria will help consume organic material and cut back on the amount of phosphorous in the water. Photos of the blue-green algae. Information about Grand Lake from Ohio Department of Health.