What is the purpose of algae?
Water beckons Minnesotans this time of year, especially our lakes. But something in it can turn us away, even if other animals and organisms need it.
"Algae does have a purpose. It's the base of the food web in aquatic environments," said Rachael Crabb, the water resources and stormwater manager for the Minneapolis Parks and Rec Board.
Crabb said tiny invertebrates, which are often barely visible to humans, eat algae.
"Those invertebrates are then in turn eaten by small fish that are eaten by bigger fish, and then eventually you have a healthy, diverse lake," she said.
Algae can look like plants, but they don't have true roots, stems or leaves, according to the Minnesota Department of Natural Resources. They form thanks to a mix of light, heat, and nutrients like nitrogen and phosphorus. Those nutrients typically enter lakes through stormwater runoff.
Tuesday afternoon, filamentous green algae were blooming on the southeast edge of Bde Maka Ska. While it might be a visual nuisance to humans, it's not toxic.
That warning is reserved for a different type of algae that technically is a bacterium.
"It's called cyanobacteria or blue-green algae. And this type of algae can actually make a lot of different chemicals and some of those chemicals are toxic to people and pets," said Crabb.
It's the reason beaches in the city might temporarily close. Crabb showed us how to check for the toxic bacteria by taking a stick and trying to stir up the growth. If it hangs off a stick, it's normal algae, but if it coats the stick like paint, it's blue-green.
"In Minneapolis, the city, the park board, lots of different organizations do projects to treat stormwater and that stormwater is a big source of phosphorus to the lakes," said Crabb. "So, as we treat phosphorus in stormwater, we reduce the amount of nutrients going into lakes."
When compared to a lake, algae are much easier to control in smaller man-made structures.
Take, for example, the lily pad pool outside the Como Park Zoo and Conservatory. A spokesperson told WCCO that they use a biological/enzyme control to prevent algae blooms that also protects the plant life. The effort costs about $3,000 to $4,000 a year.
Unlike lakes, pools can be drained to clean out algae. That's the plan for the Lincoln Memorial Reflecting Pool in Washington, D.C., where the green growth hasn't stopped despite millions of dollars in renovations.
Crabb says managing algae in natural bodies is a delicate balance of allowing nature to take its course while making sure they're accessible to people.
"We all want lakes to be fishable and swimmable. And too much algae can make it difficult to swim, but not enough algae means that your lake is almost dead," she said.
Minneapolis has two harvesting machines that can skim lakes to remove algae. However, Crabb said their impact is limited.
"Once a bloom is happening, there's not a lot that you can do," she said.
