A satellite photo of last year’s algae bloom (bright green) in Lake Erie.

The good news is that nearly 500,000 people in the Toledo, Ohio area can drink and bathe in tap water again. That’s undoubtedly a relief, after the toxin microcystin, produced by a massive algae bloom in Lake Erie, showed up in the local water supply this past weekend, forcing officials to impose a temporary water ban on Saturday. On Monday morning, Toledo mayor D. Michael Collins announced that the water was again safe, after the latest tests no longer showed detectable levels of microcystin. He proved his point by drinking a glass of water.

Officials in other nearby communities, though, maintained their own bans until they could examine the latest data. Initial tests on Saturday has showed concentrations of 1.5 to 2.5 parts per billion, above the 1.0 threshold set by the World Health Organization. U.S. Rep. Marcy Kaptur, D-Toledo, told the Toledo Blade newspaper that the level may have spiked to 3 ppb in some areas.

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That caution was well-advised, since microcystin, which can cause nausea, vomiting, visual disturbances and muscle weakness, is pretty nasty stuff.  It’s made a lot of people sick over the years, and is potentially fatal for people with other health problems. An outbreak in Brazil in 1996 killed 52 kidney dialysis patients, according to a 2009 report on microcystin by California environmental officials.

And as mayor Collins noted, the contamination crisis in Toledo was a wake-up call about the dangers of algae blooms in Lake Erie, which have been resurgent in recent years. Scientists say that agricultural phosphorus runoff is stimulating the blooms, though increased rainfall and warmer waters caused by climate change also may be playing a role in accelerating their growth. “We have not been good stewards” of Lake Erie’s water, Collins admitted.

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The big worry on everyone’s minds is that the microcystin, which managed to overwhelm an eight-step purification process at the local water treatment plant, could return this season. Laura Johnson, a research scientist at the National Center for Water Quality Research at Heidelberg University, told USA Today that the algae blooms usually reach their maximum intensity in September.  ”What’s really scary is it’s so early in the season,” she said.