On Monday, residents of Toledo, Ohio could resume using their tap water. It was deemed dangerous late last week, because of blooms in Lake Erie.
Experts detected algae blooms that can emit chemicals toxic to human health.
The blooms, which can look as if someone poured green paint on top of the water, indicate a lot of phosphorus entered the water and settled near intake pipes, according to Harvey Bootsma. He's an associate professor at UWM’s School of Freshwater Sciences.
Bootsma defines phosphorus as an essential nutrient that all plants and animals need to grow. He compares it to fertilizer you might spread on your yard or garden to make plants grow faster. It does the same in the water, which can be problematic.
"Phosphorus was a big problem in the Great Lakes back in the '60s and '70s, and a lot measures were put in place to reduce phosphorus loading to the Great Lakes, and they were largely successful. The quality of water in the Great Lakes improved dramatically in the '80s and '90s," Bootsma says.
However, since the '90s, Bootsma says the problem has returned.
"Either due to things like invasive species, like the zebra and quagga mussels in Lake Michigan, which are completely changing the way phosphorus works in the lake, or to situations like Lake Erie, where agriculture has continued to increased in intensity, and so we're now putting more phosphorus on the land than we were back in the '60s and 70s'. So a problem that we thought we had licked has come back to haunt us again," Bootsma says.
The scientist says phosphorus also continues entering Lake Michigan, but it does not face quite the same situation as Lake Erie. Bootsma says the Lake Erie watershed is more heavily populated and cultivated, on average, than is the Lake Michigan watershed. Plus, he says, Lake Michigan is not as shallow as the western basin of Lake Erie, so the nutrients present in Lake Michigan are more diluted.
Yet, Bootsma says, people who spend time along the Lake Michigan shore in Wisconsin are familiar with some phosphorus-related problems.
"Nuisance algae blooms that occur in Lake Michigan and often wash up on the shore late in the summer, creating the bad smells and the bad scenery," Bootsma says.
Boostmas says rough waters or a shift in wind direction can break up or dilute concentrations of the algae.