A prolonged heat wave in the central U.S. has fostered the growth of a dangerous form of algae in lakes and ponds, threatening swimmers and livestock and scaring away tourists during the busy summer season.

Blue-green algae are actually bacteria that produce toxins harmful to humans and livestock. It flourishes in warm, stagnant, sunlit water, and this year’s heat wave combined with Oklahoma’s worst drought since the Dust Bowl have created what one water official called a “perfect storm” for its growth.

Officials have issued a series of warnings, telling boaters and swimmers at lakes in northeast Oklahoma, southern Kansas and Nebraska to avoid contact with the toxic gunk. The issue attracted national attention earlier this month when Oklahoma Sen. James Inhofe blamed a respiratory illness on a swim in Grand Lake in Ketchum Hollow.

The bad publicity has had dire consequences for some businesses in Oklahoma where tourism is the third largest industry with an estimated annual impact of $6.2 billion. Oklahoma’s numerous lakes are a “huge economic engine” driving that industry, said Leslie Blair, a spokeswoman for the Department of Tourism and Recreation.

Problems on Grand Lake have subsided, the Grand River Dam Authority said. Advisories remained in effect Wednesday for portions of Keystone, Fort Gibson and Eufaula lakes in Oklahoma, Marion and Big Hill lakes in Kansas, and Willow Creek Lake in northeast Nebraska.

This Week's Circulars