Red Lake Watershed District Blue-Green Algae Updates

The Red Lake Watershed District began testing water in the Mud River and other lakes/rivers for blue-green algal toxins(microcystins and cyanotoxins) in response to dog deaths that were caused by ingesting blue-green algae. The District uses Abraxis kits to test the water for algal toxins. Previous blooms have been connected to high water temperatures and high concentrations of nutrients. 

The Mud River at the Grygla city park and water has been tested for blue-green algae during periods of high temperatures and low flow during the months of July through September. No positive test results for blue green algae have been discovered in the Mud River since regular monitoring began. 

Since the discovery of blue-green algae or algal toxins in lakes and reservoirs during the summer of 2018,regular sampling and monitoring has been conducted to discover algal blooms/toxins and learn more about the conditions that may lead to algal blooms. District staff regularly sampled for algal toxins in Maple Lake (once every two weeks at the public beach) because that was location of the highest concentration of algal toxins that the District had previously measured within a lake sample. If measurable concentrations are found in Maple Lake, the district is prepared to sample other shallow eutrophic lakes to find other cases of measurable or high algal toxins.   

Informational Resources


There was insufficient space in the summer 2023 RLWD staff schedule for much proactive sampling for blue-green algae toxins. Staff responded to complaints from Cable Lake (7/17/2023), Robinhood Drive in Thief River Falls (Red Lake River, 9/8/2023 - 9/11/2023), and the "Golf Course Bridge" crossing of the Thief River north of Thief River Falls (6/27/2023 - 6/30/2023). No algal toxins were found at either of those locations, but it is possible that the blooms had occurred and then dissipated before RLWD staff arrived - especially at Cable Lake where a dog reportedly became sick (and thankfully recovered) after drinking water from the lake.  


A water sample collected July 15, 2022 from the Polk County Park Marina on Maple Lake, where some potential blue-green algae had accumulated, did test positive for algal toxins (>10 mg/L). A "jar test" revealed a relatively high amount of blue-green algae. 

Due to the July 15, 2022 positive test, additional samples were collected on Monday July 18, 2022 at the Polk County Park beach and from additional lakes in the area. There was less visual evidence of blue-green algae in Maple Lake at the Polk County Park marina and no evidence at the beach. No algal toxins were found in the sample collected at the beach. The jar test sample from the beach looked very clear, with no visible evidence of blue-green algae. Hill River Lake and Badger Lake had no visual evidence of blue-green algae proliferation on July 18, 2022. The water in Cameron Lake was green, but it was mostly green algae (sank to the bottom of the "jar test" rather than floating to the top). No toxins were measured in that sample. Oak Lake had some accumulation of blue-green algae near the shore on July 18, 2022 and had a positive test for algal toxins (1-2.5 parts per billion). There clearly was some blue-green algae present in the sample after completion of a "jar test," but much less than what was in the July 15th sample from Maple Lake.     

July 29, 2022: No algal toxins present in today's sample collected from Maple Lake at the Polk County Park marina.

August 5, 2022: No algal toxins present in today's sample collected from Maple Lake at the Polk County Park marina.


Maple Lake

Maple Lake will be sampled for the presence of algal toxins once every two-weeks, at the Polk County Park marina. 

August 19, 2021: 0 ppb of algal toxins at the Polk County Park marina, no visual evidence of a bloom

August 3, 2021: 0 ppb of algal toxins at the Polk County Park marina. 

No algal toxins were found in the sample collected on July 20, 2021. The jar test showed that some blue-green algae was present in the sample. 

Thief River

The Thief River, at the "Golf Course Bridge" crossing, was checked for the presence of blue-green algae on July 20, 2021. There was a green tint to the water. Blue-green algae was noticeably present in the sample and it's presence was confirmed by a jar test. Test results showed that algal toxins were not present at a measurable concentration. 

July 26, 2021: No visual evidence of a bloom and no algal toxins at the Golf Course Bridge crossing of the Thief River. 

Red Lake River

There have been reports of blue-green algae in the Red Lake River. The location and severity are unknown. There was no visual evidence of a bloom on July 26, 2021. 

Thief River

The Thief River maintained enough flow in 2020 to avoid the stagnant conditions that led to a blue-green algae bloom in 2018. The golf-course bridge will be monitored each year for signs of a bloom if there are low-flow conditions and warm temperatures during the months of July and August. 

Maple Lake

Intense, but localized blue-green algae blooms were found in Maple Lake during the summer of 2020. The intense, visible blooms occurred along areas of sheltered shoreline (a marina, for example) on the south eastern end of the lake. Samples collected from open water areas did not have measurable concentrations of algal toxins. A detailed description of monitoring results can be found in the 2020 Red Lake Watershed District Annual Report, starting on Page 60. 

Other Lakes

Intensive sampling of shallow and eutrophic lakes was triggered by the confirmation of a blue-green algae bloom in Lake Sarah (in the Sand Hill Watershed District, but not far from the Red Lake Watershed District boundary. An intense, lake-wide blue-green algae bloom was found in Oak Lake. No toxins were found in Badger Lake and Hill River Lake. 

The Mud River, Maple Lake, and Hill River Lake were tested for algal toxins during the summer of 2019. No blue-green algae blooms or algal toxins were found/reported within the Red Lake Watershed District during the summer of 2019. 

Cameron Lake

An algal toxin concentration in the range of 2.5-5 parts per billion was found in Cameron lake on August 13, 2018. 

Maple Lake

In response to complaints about algae in Maple Lake, water samples were collected and send to a laboratory for algae identification. The sample was dominated by diatoms and green algae (Spirogyra, not harmful). However, the lab also noted that blue-green algae was present. Additional samples were collected throughout the rest of the summer and analyzed for algal toxins. A concentration of 5 mg/L (low risk) was found on July 6, 2018 and July 27, 2018. A lower concentration (0-1 mg/L) was found  on August 24, 2018.   

Thief River

On Friday, Jul 13, 2018, a significant blue-green algae bloom was found in the Thief River near the Thief River Golf Club. News of the bloom was shared with the city, law enforcement, state agencies, and other local agencies. RLWD staff were interviewed by local media. Warning signs were placed in public parks and accesses. The city of Thief River Falls closed the beach. A no-wake ordinance was created along the Thief River to reduce the amount of nutrients that were being stirred-up by boat traffic. Despite the very obvious bloom and potential hazard, algal toxin concentrations were below the measurable level in all samples collected by the RLWD. The bloom dissipated in August, with the arrival of cooler weather. 

 2015- 2017

Lorem Ipsum

In 20XX, two dogs died from blue-green algae poisoning after drinking from the Mud River in Grygla. Testing confirmed the presence of blue-green algae. Since then, the Red Lake Watershed District has sampled the Mud River, at the Grygla City Park, for the presence of algal toxins. No measurable concentrations have been recorded in the years since the incident. 

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