Crooked Lake Water Testing

Blue-green Algae Bloom

Updated 7-21-23

Crooked Lake remains under a water advisory. 

June 14, 2023The City of Coon Rapids was first notified by the Coon Creek Watershed District on 6-14-23 that a report of blue-green algae bloom was detected on Crooked Lake. Blue-green algae blooms are harmful when they produce toxins that can make humans and animals sick.
July 20, 2023The City of Coon Rapids received cyanotoxin test results, which were collected on 7-12-23. Results were within the recommended levels established by the MPCA and did not indicate an elevated risk at the time of testing.*

*There is no single approach for evaluating and making decisions regarding the presence and potential threat of harmful algae blooms in bodies of water. Testing surface water for cyanotoxins (toxins produced by blue-green algae) provides the best measure to assess the public health risk from harmful algae blooms (HABs) and inform health-protection decisions. The results reflect conditions at the time the sample was collected; conditions may change quickly, sometimes even before the test results are available.

There is no way to tell if a blue-green algal bloom is toxic just by looking at it. Adults, children and animals should avoid contact with water with blue-green algae. Toxins can persist in the water after a bloom; watch for signs of recent blooms, such as green scum on the shoreline. When in doubt, stay out! If you or your pet go into water where there may be a bloom, wash off with fresh water immediately afterwards.

Signs detailing the information below are posted at Crooked Lake Park. 


The water in Crooked Lake may contain blue-green algae that can be harmful to humans and pets.

To reduce the risk of illness:

  • Do not swim, waterski, or tube if the water looks like spilled green paint or pea soup.
  • Avoid swallowing water and watch small children and pets who may ingest water.
  • Rinse off with clean water after swimming.
  • Stay away from areas of scum when boating.

Contact your healthcare provider or veterinarian if you or your pet become sick after swimming.


Photos show examples of what blue-green algae looks like. 

Though often referred to as algae, blue-green algae are not algae at all, but types of bacteria called cyanobacteria. They are normally present in bodies of water and common in Minnesota. This type of bacteria thrives in warm, nutrient-rich water. When conditions are right, the blue-green algae can grow quickly forming “blooms.” Certain varieties of blue-green algae can produce toxins that are linked to illness in humans and animals.

For more information about blue-green algae, visit the Minnesota Pollution Control Agency's website.

E.Coli Testing

City staff tests for E. coli levels at the water access at Crooked Lake Memorial Day weekend through Labor Day weekend. This initiative started July 29, 2019 after renovations at Crooked Lake Park were complete. Crooked Lake Park offers water access, with a small, sandy area that is available for the public to enjoy. No lifeguards are on duty and any swimming is at your own risk.

If E. coli levels exceed the standards set by the Minnesota Pollution Control Agency (MPCA), the water access will be closed temporarily until the readings return to a safe level. Information about the Minnesota state rule referencing E. coli levels for recreational waters is found below:

Minnesota Rule 7050.0222 Specific Water Quality Standards for Class 2 Waters of the State; Aquatic Life and Recreation: E. coli levels not to exceed 126 organisms per 100 milliliters as a geometric mean of not less than five samples representative of conditions within any calendar month, nor shall more than ten percent of all samples taken during any calendar month individually exceed 1,260 organisms per 100 milliliters. The standard applies only between April 1 and October 31.

Read more about water quality standards as recommended by the Minnesota Pollution Control Agency here.

What is E. coli?

E. coli is short for Escherichia coli, the scientific name for a group of bacteria found in the intestines and feces of warm-blooded animals such as mammals and birds. While most of the hundreds of strains of E. coli are harmless (one notable exception associated with food contamination is E. coli O157:H7), their presence can indicate sewage or feces-contaminated water which may include pathogens (disease-causing organisms).

Direct testing for pathogens is expensive and impractical, as pathogens are rarely found because they usually occur sporadically and at low levels. Instead of testing for the pathogens themselves, public agencies test for the presence of "indicator" species, so called because their presence indicates that sewage or fecal contamination may have occurred. The two most commonly used indicators for recreational waters are fecal coliforms and E. coli.

Interpreting the Results

Samples are collected weekly from Crooked Lake with results listed in the table below. If E. coli levels exceed those recommended by the state, the water access area will be closed temporarily until further testing shows safe levels.

Conditions which impact E. coli levels include rainfall (materials harboring the microorganisms can be washed into the water from the surrounding landscape), concentrated waterfowl numbers (one reason why feeding waterfowl is prohibited), and high temperatures. For more information call 763-767-6576.

Table 1. E. coli Test Results for Crooked Lake (taken at water access area off 13180 Crooked Lake Blvd.) 

Results are given in MPN/100 ml (approximate number of viable cells per 100 milliliters, MPN stands for Most Probable Number), and geometric means will become available after more testing is complete as time goes on. As the City continues to monitor bacteria levels, determinations will be made as to when single testing levels exceed the standards to close the water access area.

Current Bacteria Results as of July 2023: The test results are meeting the Minnesota standard for recreational waters.

Crooked Lake Bacteria Test Results

Test Date Test Results Test Location
June 1, 2023 First test of 2023 2 MPN/100 mL Crooked Lake Water Area
June 7, 2023 21.5 MPN/100 mL Crooked Lake Water Area
June 13, 2023 1 MPN/100 mL Crooked Lake Water Area
June 22, 2023 5 MPN/100 mL Crooked Lake Water Area
June 29, 2023 3.5 MPN/100 mL Crooked Lake Water Area
July 12, 2023 1 MPN/100 mL Crooked Lake Water Area
July 17, 2023 7 MPN/100 mL Crooked Lake Water Area
July 24, 2023 6.5 MPN/100 mL Crooked Lake Water Area
Aug. 2, 2023 5.2 MPN/100 mL Crooked Lake Water Area
Aug. 7, 2023 12 MPN/100 mL Crooked Lake Water Area
Aug. 16, 2023 45 MPN/100 mL Crooked Lake Water Area