Harmful Algal Blooms (HABs)

Different types of naturally-occurring algal blooms may be seen on lakes and rivers. Most are not harmful. However, there are some that are made of cyanobacteria that have the ability to produce toxins, causing a harmful algal bloom (HAB). These blooms can last a few days, weeks, or longer, and are considered harmful because they may contain cyanotoxins. A bloom can start out small, become very large in size, and may give off a bad odor. 

Map of Verified HABs

Reports of cyanobacterial blooms and results of cyanotoxin testing in Michigan can now be found online at the Michigan Harmful Algal Bloom Reports map. The map will be updated once per week during June through November and shows locations of verified bloom reports and results of any cyanotoxin tests conducted by the state or local health departments, and other partner agencies. Note that not all HABs in Michigan are reported to the state, so every bloom may not be included on the map. HABs can move around, disappear and reappear – meaning that HABs may be present in waterbodies, but not present on the map. Before going in any water, always look for and keep away from visible HABs or scums and that people and pets stay out of water in affected areas.

Local advisory: Pleasant Lake, Manchester MI, May 2023

What does a HAB look like?

Not all algal blooms have cyanotoxins, so it is difficult to tell if it is harmful by looking at it. HABs can be a variety of colors such as green, blue-green, blue, brown, yellow, white, purple, or red. HABs can look like scums in the water and may have small flecks, foams, or sometimes globs and mats floating in it. The water can also look like it has spilled paint or a green sheen on the surface. 

See the Michigan Harmful Algal Bloom Picture Guide.

What are the health risks of HABs?

HABs form due to a rapid growth of cyanobacteria, also called blue-green algae, which are naturally found in lakes, rivers and ponds. Toxins found in cyanobacteria (cyanotoxins) that can be found in blooms can be harmful to people and animals. 

  • Skin contact with HABs may cause irritation such as rashes, hives, or skin blisters. It may also cause runny eyes and nose or asthma-like symptoms. 
  • Contact with the airborne cyanotoxins in the spray may cause skin, eye, nose, or throat irritation. 
  • Swallowing large amounts of water having cyanotoxins in it may cause stomach pain, vomiting, diarrhea, weakness, numbness, headaches, dizziness, or difficulty breathing. Frequently swallowing or swallowing large amounts of cyanotoxins can harm the liver or kidneys. 

If you may have had contact with or swallowed water containing cyanotoxins, and have any of the symptoms listed above, talk to your doctor or call Poison Control at 800-222-1222. If symptoms are severe, get emergency medical attention as soon as possible. 

What should people do if they think they have found a HAB? 

If people think they have found a HAB or have any suspicion of a HAB: 

  • Do not let people, pets, or livestock in the water or near the shore in affected areas. Avoid direct contact or swallowing water in an area with a visible algae bloom. This includes swimming, boating, tubing, skiing, playing in or allowing pets in the water in active bloom areas.
  • If no scum is visible, but you are unable to see your feet when standing knee deep (after sediment has settled), avoid bathing, immersion of your head, or ingesting.
  • Always rinse off people and pets after contact with any lake or pond water. 
  • If there is a posted HAB advisory or closing, follow the instructions. 
  • You can still use unaffected areas of a lake, unless a bloom covers most of the lake. People and pets should avoid the water entirely, including fishing and boating activities, if there is a large HAB spread out across the waterbody. 
  • Report suspicious looking algae to the Michigan Department of Environment, Great Lakes, and Energy (EGLE) by calling the Environmental Assistance Center at 800-662-9278 or emailing [email protected].

What can we do to prevent HABs?

Algal blooms are a normal part of lake and pond cycle. Harmful algal blooms need sunlight, slow-moving water, and nutrients, like nitrogen and phosphorus. Nutrient pollution from human activities makes the problem worse, leading to more severe and more frequent blooms. You can help reduce nutrient pollution by:

  • Choose phosphate-free detergents, soaps, and household cleansers.
  • When walking your pet, pick up after them and keep their waste away from waterways and waterbodies.
  • Inspect your septic system annually to ensure proper function.
  • When washing vehicles and watercraft, use nontoxic, phosphate free soaps and wash them on grass of gravel to filter the runoff before it enters the lake or stream.

Additional Information