Watershed pollution will feed the algae in Grand Lake St. Marys for years, according to an article by The Columbus Dispatch's Spencer Hunt.  Hunt writes:


The toxic algae problems that Lake Erie and Grand Lake St. Marys face are mirrored in lakes in Florida, China and New Zealand.
A group of international algae experts said yesterday that there are no quick or easy solutions to clear algae from lake water. In the case of Grand Lake St. Marys, it could take decades.
“ Restoring a system like that isn’t going to happen tomorrow,” said Harry Gibbons, a senior limnologist with Seattle-based Tetra Tech.
Gibbons spoke about the western Ohio lake’s blue-green algae woes at the EcoSummit 2012 conference at the Greater Columbus Convention Center.
Grand Lake St. Marys was included with China’s Lake Taihu, Florida’s Lake Okeechobee and New Zealand’s Lake Rotorua, all of which suffer from summertime “blooms” of toxic blue-green algae.
The algae, also called cyanobacteria, are common in most lakes but grow thick feeding on phosphorus from manure, fertilizers and sewage that rains wash into nearby streams. They can produce as many as four liver and nerve toxins that can sicken people and kill pets.