Blue-green algae blooms present at three Minneapolis lakes

Since May 15, when the Minneapolis Park and Recreation Board (MPRB) reported on a likely harmful algae bloom (HAB) at Cedar Lakeblue-green algae has been confirmed at Lake Nokomis and Lake of the Isles, as well as Cedar Lake. MPRB is advising that people and pets stay out of the water when these blooms are visible. 

 

Contrary to its name, blue-green algae can turn lake water into a murky brown color, as it has on these three lakes. Blue-green algae is actually a bacteria that is that is normally present in many lakes throughout the state and country. When conditions are right, this naturally forming bacteria can grow quickly, forming blooms throughout all or portions of a lake. 

 

Blue green algae can produce cyanotoxins, which can make humans and animals sick, particularly if ingested. According to the Minnesota Department of Health (MDH), symptoms of illness from blue green algae can include vomiting, diarrhea, rash, eye irritation, cough, sore throat, and headache. Symptoms generally begin several hours up to 2 days after exposure. 

 

The MPRB is posting warning signs on the shorelines of all three lakes and at connecting channels.  

About Harmful Algae Blooms (HABs) 

There is no way to tell if an algae bloom is toxic just by looking at it. Therefore, the MDH advises the following: 

  • Don’t swim if you can’t see your feet in knee-high water.   
  • If you’ve recently been in contact with an algae bloom, make sure to wash off with fresh water. 
  • When in doubt, stay out!  
  • Don’t let dogs drink or swim in the water. *
  • For more information on minimizing your risk of exposure to blue-green algae and harmful algal blooms from swimming, boating, or consuming fish, visit the MDH website: https://www.health.state.mn.us/diseases/hab/prevention.html* Note: Dogs are not allowed in Minneapolis water bodies, per MPRB ordinances.

Why is this happening? 

Algae are a natural part of lake ecology, and as weather and lake conditions change, different types of algae can grow. The species of algae currently blooming grows better in cooler conditions. 

Plankton samples MPRB collected last winter show that the algae blooms at these three lakes started under the ice. In a normal year, ice would melt off slowly and the algae would die off before it got a foothold in the lake. This spring, a rapid ice-out and cooler than average temperatures led to conditions that allowed the algae to persist. These blooms will diminish or subside as air and water temperatures rise. 

The MPRB continues to monitor the algae blooms in Cedar Lake, Lake of the Isles and Lake Nokomis, and the water quality at all other lakes in the Minneapolis park system. 

Updates will be shared as new information becomes available, and if algae blooms at any lake in the park system are deemed potentially harmful.  

More information 

MDH: Preventing Harmful Algal Bloom-Related Illness www.health.state.mn.us/diseases/hab/prevention

MDH Fact Sheets

Harmful Algal Blooms (HABs) – English (PDF)

Harmful Algal Blooms (HABs) Hmong (PDF)

Harmful Algal Blooms (HABs) Somali (PDF)

Harmful Algal Blooms (HABs) Spanish (PDF)