The water supply in Toledo, Ohio, has returned to normal after high levels of the toxin microcystin caused the city to warn resident against using the water early Saturday.
The warning came after tests at one treatment plant showed readings for microcystin above the standard for consumption, most likely from algae on Lake Erie. Ohio Gov. John Kasich declared a state of emergency.
As the threat in Toledo passes, the event has left many wondering if it could happen again, especially because an estimated 25 million people in the United States live near the Great Lakes.
Here's what you need to know about microcystin.
What Microcystin Does: The bacteria released from algae blooms can cause liver damage. On the skin, it produces rashes, hives and blisters, according to the Minnesota Department of Health. When swallowed, it can cause stomach pain, nausea, vomiting, severe headaches and fever. There have been no known human deaths from microcystin, though it has killed pets and wildlife, according to the California Environmental Protection Agency (PDF).
What Causes Microcystin: Warm, wet weather prompts the growth of blue-green algae blooms, according to the Iowa Department of Public Health (PDF). Phosphorus from agricultural runoff feeds the growth of these blooms, according to the National Oceanic and Atmospheric Administration (NOAA). Not all algae blooms are toxic. You cannot tell whether a bloom is toxic by looking at it.
In the months and weeks before Toledo's ban on drinking water, environmental groups and water researchers have been calling on Ohio and other states in the Great Lakes region to drastically reduce the amount of phosphorus flowing into Lake Erie. Ohio lawmakers this past spring took a step toward tackling the algae problem when they enacted a law requiring most farmers to undergo training before they use commercial fertilizers on their fields. But they have stopped short of mandating restrictions on farmers.
The International Joint Commission, an advisory agency made up of Canadian and U.S. officials, said last year urgent steps are needed to reduce phosphorus applied to fields, suggesting among other things that states ban the spread of manure on frozen or snow-covered ground. It's been estimated that agricultural runoff has been contributing to algae in Lake Erie for more than a decade.
A Summer Threat? Even after cooler weather causes the collapse of summer algal blooms, microcystin can remain in the water, the Iowa Department of Public Health warns on its website.
The Problem is Getting Worse: Nutrient enrichment and climate change is causing "an apparent increase in the toxicity of some algal blooms is freshwater lakes and estuaries around the world," Oregon State University scientists said last year in the journal Science. Rising temperatures and carbon dioxide concentrations contribute to the problem.
Other Cities Risk Microcystin: The EPA considers harmful algal blooms to be a "major environmental problem" in all 50 states. NOAA and other groups help identify toxic algae outbreaks, and local municipalities in at-risk areas, such as Toledo, test their water supplies for the toxin. No federal community health standards exist for cyanotoxins, though some states have regulations based on World Health Organization guidelines, according to the Minnesota Department of Health.
Almost a year ago, one township just east of Toledo told its 2,000 residents not to drink or use the water coming from their taps. That was believed to be the first time a city has banned residents from using the water because of toxins from algae in the lake.
Information from The Associated Press contributed to this report.
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