Reports of harmful algal blooms have increased in Michigan in recent years, and state officials have tips on how to keep an eye out for them.

Algal blooms are rapid increases or accumulations of algae in surface waters, and mostly occur in lakes during summer and into fall. Cyanobacteria, known as blue-green algae, can sometimes produce toxins.

Gary Kohlhepp, supervisor of the Lake Michigan Unit for the Department of Environment, Great Lakes, and Energy, said they are the biggest human health concern when it comes to algal blooms. He pointed out in the vast majority of cases, an algal bloom shows up as scum on the surface of the water.

“Whenever you see those conditions, we advise people not come into contact with it, and also to not allow their pet to swim in it,” Kohlhepp recommended. “When in doubt, stay out. If you’re not sure whether it’s cyanobacteria or green algae, the best course of action is just to avoid it.”

Skin contact with cyanobacteria can cause rashes, hives, skin blisters or runny nose or asthma-like symptoms. Swallowing large amounts can lead to flu-like symptoms, gastrointestinal issues or neurotoxic symptoms such as harm to the liver or kidneys.

Kohlhepp noted while algae are naturally occurring, blooms are often caused by agriculture or lawn fertilizer running from farms or land into waterways. The phosphorous and sometimes nitrogen in fertilizers can be a good source of food for algae, Kohlhepp stressed, sometimes too good.

“If there’s a lot of food and especially when the weather warms up, so you get warmer temperatures, you get a lot of sunlight, not a lot of wind blowing, so it’s pretty still calm conditions,” Kohlhepp outlined. “That’s a perfect recipe for these algae to really grow like crazy. “

Kohlhepp added algal blooms often last just a short time, for a few days or up to a week, and in rare cases multiple weeks. He cautioned there is a perception the blooms are everywhere, but it is actually a small number of lakes compared with the more than 10,000 lakes in Michigan.