National Geographic : 1973 Aug
lampreys during the 1950's had virtually wiped out the lake trout population and sharply reduced other commercial and game fish. Happily, discovery of a chemical especially toxic to lamprey larvae has brought the menace largely under control. three Great Lakes are in more serious trouble. In many places they are overfertilized oversupplied with nitrogen and phosphorus. Plants, mostly algae, thrive on that diet. Where do the chemicals come from? Vir tually every sewage-treatment plant on the Great Lakes adds its share. Even after sewage has been treated, much of the "purified" water that flows back into the lake is high in nitrogen and phosphorus. Industrial effluent often contains those chemicals too. Another source is farmland. Rain washes chemical fertilizers-which almost invariably include the two nutrients-off fields into streams that feed the lakes. Drainage from farm feedlots adds animal wastes. In overfertilized waters, algae can multi ply with frightening speed. When the thick mass dies, it decomposes and soaks up pre cious oxygen from the water. At the University of Michigan in Ann Arbor, research oceanographer Dr. John C. Ayers talked about algae. "The algae bloom rhythm is getting faster and faster," he told me, "like a quickening beat on a kettledrum. It may become continu ous. We've seen it in Lake Erie and Lake On tario. Now we're beginning to see the same pattern in parts of Lake Michigan." Dr. Ayers pointed out that solutions to the problem would not be easy. "First we'd have to limit the nutrients coming in," he said. "Then we'd have to remove quantities of the nutrients already present. There's been dis cussion of removing the algae for use as fer tilizer or food, but that would take a great The Great Lakes: Is It Too Late?