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A sample glass of Lake Erie water is extracted near the City of Toledo water intake crib on Sunday. Photograph: Haraz N Ghanbari/AP
The toxins that contaminated the water supply of the city of Toledo – leaving 400,000 people without access to safe drinking water for two days – were produced by a massive algae boom. But this is not a natural disaster.
Water problems in the Great Lakes – the world’s largest freshwater system – have spiked in the last three years, largely because of agricultural pollution. Toledo draws its drinking water from Lake Erie.
Residents were warned not to drink the water on Saturday, after inspectors at the city’s water treatment plant detected the toxin known as microcystin. The toxin is produced by microcystis, a harmful blue-green algae; it causes skin rashes and may result in vomiting and liver damage if ingested. It has been known to kill dogs and other animals and boiling the water does not fix the problem; it only concentrates the toxin.
The current bloom of microcystis is concentrated in Maumee Bay in Lake Erie’s western basin, according to the National Oceanic and Atmospheric Administration (NOAA). A second, smaller bloom has appeared in Sandusky Bay.
The main cause for such algal blooms is an overload of phosphorus, which washes into lakes from commercial fertiliser used by farming operations as well as urban water-treatment centres. Hotter and longer summers also promote the spread of the blue-green scum.
The US government banned phosphorus in laundry detergents in 1988. That stopped the algal blooms for some time. But they came back to the Great Lakes in force in 2011 – forming a green scum that covered 5,000 square kilometres (1,900 sq miles) of water at its biggest extent – in the worst algal bloom in recorded history.
Scientists attribute the comeback in large part to changes in farming practices, including larger farms and different fertiliser practices, which send heavier loads of phosphorus into the lakes.