7/16/2025
Keatons Lake HAB Update and Response Summary:
UPDATE 7/16/25:
Post-treatment water samples collected on July 8 (after the first algaecide treatment on July 2) showed an average potentially toxigenic cyanobacteria (PTOX) cell density of 1,190 cells/mL, with the highest result at 1,500 cells/mL across three testing locations.
These results indicate the treatment was effective in reducing algae levels.
Consistent with LOWA’s HAB Response Plan and out of an abundance of caution, the lake will remain closed until a second round of testing confirms that PTOX cell counts remain below the safe threshold for reopening.
Next steps:
- A second set of water samples was collected by LOWA staff on July 15 and submitted to the lab.
- Results are expected by the end of Friday, July 18, or early next week.
- Today, July 16, SOLitude Lake Management is conducting the second phase of the two-part algaecide treatment.
Per LOWA HAB Response Plan, reopening Keatons Lake requires:
- Waiting at least 48 hours after treatment for product efficacy.
- Conducting post-treatment testing to confirm reduced PTOX levels.(samples collected 7/7) RESULTS NOTED ABOVE.
- Conducting a second round of testing approximately one week later. (samples collected 7/15)
- Ensuring all sample results fall below closure and advisory thresholds. (LOWA HAB Response Protocol, Lake Closure threshold exceeding PTOX 50,000 cells/mL and Advisory Level threshold exceeding PTOX 10,000 cell/mL)
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RESPONSE SUMMARY:
Lake of the Woods Association follows a Harmful Algal Bloom Response Protocol, which outlines monitoring and treatment procedures from June through September. As part of this protocol, regular algae identification testing is conducted to track concentrations of potentially toxigenic cyanobacteria (PTOX).
The response plan includes the following thresholds:
Treatment recommended when concentrations reach 20,000–50,000 cells/mL.
Lake closure triggered when concentrations exceed 50,000 cells/mL.
Below are the most recent testing results for Keatons Lake:
May 28, 2025 – 9,800 cells/mL
June 13, 2025 – 6,400 cells/mL
June 19, 2025 – 4,310 cells/mL
June 25, 2025 – 89,900 cells/mL
As indicated above in the testing results, we experienced a significant spike in PTOX levels between June 19 and June 25—leaping from the “green” category (below 10,000 cells/mL) to well into the “red” category (above 50,000 cells/mL), which requires immediate lake closure. Referencing the Water Quality Testing Parameters: Algal Blooms in the Response Protocol.
This sudden increase is likely the result of several consecutive weather events, including heavy rainfall (which introduces nutrient runoff into the lake) followed by a stretch of high temperatures—ideal conditions for algae to proliferate rapidly.
Although the June 19 sample showed relatively low PTOX levels, in anticipation of potential growth and the upcoming holiday, we proactively scheduled SOLitude Lake Management to perform a treatment on July 2, 2025, with a follow-up treatment 10–14 days later.
According to SOLitude, the HAB treatment product remains effective for approximately 48 hours, so scheduling too early would allow time for regrowth before the July 4th weekend.
Despite our proactive planning, the rapid rise in cell counts between testing dates surpassed our expectations and required immediate closure.
Next Steps and Reopening Protocol:
Per our HAB Response Plan, reopening Keatons Lake requires:
- Treatment Application (Completed July 2)
- Wait 48 Hours for treatment to take effect.
- Post-Treatment Testing to confirm reduced levels. Algae samples were collected 7/7/2025. (Timeline on receiving algae results have been more variable than E. coli results, taking about a week.)
- Follow-Up Testing one week later.
- Verification that levels are below closure and advisory thresholds.
This process meant that Keatons Lake remained closed through the July 4th weekend to allow time for safe treatment and validation.
We understand this is disappointing for members, but we remain committed to prioritizing public health and safety in accordance with our established environmental protocols.
We will continue to keep the community informed as we monitor progress and await post-treatment results.
To follow our Beach and Lake Statuses which includes water testing results click HERE.
To Learn More about Harmful Algal Bloom (HAB) and FAQ about HAB explore the Virginia Department of Health (VDH) Swim Healthy, Virginia webpage Click HERE.
To Access the Keatons Lake Harmful Algal Bloom Response Protocol Click HERE
