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The Season of Algae Blooms

26 Sep 2019 9:00 PM | Natalie Love (Administrator)

Harmful Algae Blooms (HABs) are not only a rapidly growing environmental and health concern but are increasingly being broadcasted in the news and raising public concerns. Hearing about a resident or pet’s health issues from a local lake can make you ask yourself, could this happen in my city’s local body of water and am I prepared to resolve the issue?

Finding solutions to drinking water problems caused by algae is an ongoing challenge to the water industry from taste and odor, to filter clogging Diatoms, to harmful algal blooms of toxin-producing cyanobacteria. There is a widespread belief that the frequency and severity of surface water impairment by algae is increasing due to human impact, leading to higher nutrient levels in-stream and increased eutrophication. Algae may also be linked to droughts and the result of climate change. In addition to drinking water quality, there are growing concerns for lake and reservoir ecosystems.

The EPA and CDPHE are moving in the direction of additionally creating more recreational guidelines and regulations to monitor concentrations of certain blue green algae, mainly Cylindrospermopsin, Anotoxin-A, and Microsystins. Dependent on whether the body of water must meet swimming standards or recreational standards, there are different guidelines for criteria excursions.

The Environmental Protection Agency recommends the criteria in Table 1, but it is up to individual states to adopt these criteria. Table 2 summarizes the World Health Organization’s recreational guidance and action levels.

Table 1: Recommended recreational criteria and swimming advisory criteria. Swimming advisory not to exceed on any day and recreation criteria not to exceed more than 10 percent of days per recreational season.



8 ug/l

15 ug/l

Table 2: WHO recreational guidelines.

Relative probability of Acute Health Effects

Cyanobacteria (cells/mL)

Chlorophyll a (ug/L)

Estimated Microcystin Levels (ug/L




< 10



10 - 50

10 – 20


>100,000 – 10,000,000

50 – 5,00

20 – 2,000

Very High




If these numbers indicate a potential risk or vulnerability of HABs, it is recommended that your organization start implementing or update a proactive plan or SOP to monitor local lakes. This can be done in conjunction with local Parks Departments and/or water utilities department members. Monitor and set levels of concentrations at which potential risk for relative probability of acute health effects could affect the public. Look at modifying warning signs to prevent public contamination, research treatment options, and identify species with the CDPHE lab or a private lab to know for certain what you are dealing with. Check out CDPHE’s “Algae bloom risk-management toolkit for recreational waters” for more help in managing risk.

There are options for treatment and monitoring that are becoming more advanced but also expensive. Chemical treatment has always been an option but is a recurring expense that might cause more harm to the ecological environment and potentially a temporary release of toxins depending on chemical solutions and concentrations. The addition of dissolved oxygen through blowers, aerators or mixers are all treatment options but also could come with energy costs. Ultrasonic treatment is another option but is depended on surface area of the body of water.

Ultimately, it is a growing issue of concern, like all other emerging contaminants like TENORM and PFAS that needs more research and technology to mitigate the issue and understand prevention of toxin production, monitoring and identifying strategies and possible treatment options for the goal of public health and safety.

John Winterton works for the City of Northglenn as the Laboratory Supervisor. He's been with Northglenn for 3.5 years for lab and operations but recently moved to his current position. Prior to that, he worked as a lab technician for the Chicago land area for 5 years. He holds a Class A wastewater license in Colorado and a Class B Water for Illinois. John is not an expert in the field of HABs and identifying algae species, but he has taken on the topic as it has been a growing concern in Northglenn and statewide.


CDPHE Algae Bloom Risk-Management Toolkit

EPA Recommendations for Cyanobacteria and Cyanotoxin Monitoring in Recreational Waters

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