TOLEDO, Ohio — The toxic algae that spread across Lake Erie this summer roughly matched its third-most severe bloom in 15 years, government researchers said earlier this week.
The algae outbreak on the shallowest of the Great Lakes had two peaks this year in August and again in mid-September, according to the National Oceanic and Atmospheric Administration.
It left behind a thick, paint-like scum on the surface that had covered about 280 square miles by September, but the entire bloom was much larger and stretched from Toledo to the shoreline along Ontario, Canada and reached the mouth of the Detroit River, the agency said.
It also was less toxic than in past years, scientists said.
Researchers said it was roughly equal to the one in 2013 and much smaller than the record-setting outbreak in 2015.
The potentially toxic algae blooms that are fed by farm fertilizer runoff and municipal sewage overflows are a threat to drinking water, aquatic life and tourism.
Only twice have the blooms fouled public water supplies along western Lake Erie, but several cities must treat their water with chemicals each summer to combat the toxins.
A smaller bloom in 2014 settled over Toledo’s drinking water intake pipe in the lake and contaminated the supply for just over two days.
The bloom a year ago was relatively mild because of dry weather.
But heavy rains during the spring and early summer this year washed tons of fertilizer from farm fields into the streams and rivers that flow into the lake. Phosphorus in fertilizers, livestock manure and raw sewage feed the algae.
While steps have been taken to reduce the farm fertilizer runoff and municipal sewage overflows that feed the algae, environmental groups and some political leaders have been frustrated by the pace and depth of those efforts.
Two federal lawsuits have been filed to force the U.S. Environmental Protection Agency to take more action.