Algae risks grow in Arizona lakes amid testing gaps

Arizona’s lakes are seeing more algae blooms that pose risks to wildlife and public health, yet inconsistent testing leaves gaps in tracking potential hazards.

Last summer, a series of viral videos circulated online showing dogs suddenly dying after swimming in lakes contaminated with blue-green algae. The alarming trend raised questions about water safety not just for pets, but for people who frequent Arizona’s lakes and rivers during the hottest months of the year.

Prompted by these concerns, a public records request was filed with the Arizona Department of Environmental Quality to examine how often state agencies were testing for harmful algal blooms. The findings revealed troubling gaps in oversight — and raised deeper questions about how well Arizona is monitoring the health risks in its most popular recreational waters.

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Algae blooms in Arizona lakes are becoming a frequent sight, and they’re raising alarms for both wildlife and the people who enjoy these waters. The Arizona Department of Environmental Quality (ADEQ) and recent lab reports highlights the state’s algae testing patterns, growing public concerns, and ADEQ’s call for better awareness of algae-related risks.

A Growing Concern: Blue-Green Algae in Arizona

Since early 2022, Arizona lakes have been seeing more testing for blue-green algae, a type of cyanobacteria that, in some cases, can produce toxins harmful to animals and humans. According to ADEQ, lakes across the state were tested between January 2022 and July 2024 by different agencies, from state and local government departments to regional water boards and national forests. Key lakes tested included popular sites like Lake Havasu, Saguaro Lake, and Bartlett Lake. Though cyanobacteria tests are not required by law, managers of these lakes voluntarily performed testing due to public health concerns.

Golden algae, a separate species known to cause fish kills, was also detected in places like Canyon Lake. Testing in March 2024 at popular areas such as Beer Can Point and Cutout Cove confirmed the presence of golden algae. These findings came shortly after a fish kill that left around 1,000 dead shad fish floating in the lake, highlighting the impact that unchecked algae growth can have on aquatic life.

What Testing Reveals (and What It Doesn’t)

The ADEQ’s data shows a mix of voluntary and agency-led efforts to monitor algae levels, though gaps remain. In several lakes, tests showed levels of cyanobacteria below dangerous thresholds, and no cyanotoxins (the toxins released by cyanobacteria) were found in drinking water samples from the cities of Flagstaff and Prescott Valley. Samples from Flagstaff’s Upper Lake Mary in July 2023 confirmed no detectable levels of toxins like anatoxin-a and microcystins, suggesting safe conditions for human recreation and water use. Similarly, the Bartlett Lake report from June 2023 showed no harmful toxin levels.

Despite these reassuring findings, not all lakes are consistently tested. ADEQ’s statement points out that testing is not required in Arizona; rather, it’s up to lake managers to decide. Lake managers rely on their own judgment and available resources to test for cyanobacteria, which means there are times when algae may be present, but not documented, in some waters.

This variability in testing can impact public perception of water safety. ADEQ has encouraged lake managers to post signs in both English and Spanish warning visitors of possible health risks during suspected bloom periods. ADEQ is especially concerned because scientists are still learning about cyanotoxins and how they may impact health. According to ADEQ, “it is not yet known how many different cyanotoxins exist” and how severe their effects may be. This uncertainty, paired with the sporadic testing, can leave recreational visitors with unanswered questions.

Canyon Lake’s Fish Kill: A Closer Look

One of the most noticeable impacts of algae blooms in Arizona is the harm to fish populations. In March 2024, golden algae was identified as the likely cause of a fish kill that left approximately 1,000 shad fish dead in Canyon Lake. Areas such as the Marina and Dam also showed algae presence, with common types like Anabaena, which has been known to produce toxins in some cases. While Canyon Lake’s algae levels have not posed a health risk to humans, the fish kill shows that these blooms can still have a serious environmental impact.

Lake Havasu and the Need for Precaution

Testing at Lake Havasu in late 2022 showed high levels of microcystin, a type of cyanotoxin that can be harmful to both animals and humans. One specific site, the Havasu State Park PWC Launch Ramp, recorded microcystin levels as high as 2,606 micrograms per liter—levels that ADEQ considers “high risk” for exposure. However, even in cases like this, where harmful levels of toxins are detected, ADEQ does not have the authority to require action by lake managers. Instead, they encourage lake owners and managers to inform the public and take preventative steps.

ADEQ has explained that lake managers must handle their own testing procedures and results, including sampling, lab work, and payment. ADEQ assists by providing guidance on testing methods, but any measures taken, like putting up public warnings or closing sections of the lake, are ultimately up to lake management.

The Importance of Testing and Reporting

One clear takeaway from ADEQ’s report is the importance of regular, consistent algae testing. ADEQ emphasizes the need for testing, especially during warmer months, when blooms are more likely. Agencies and lake managers are also encouraged to share their test data with ADEQ and the Arizona Game and Fish Department (AZGFD) to keep track of cyanobacteria trends and potential risks. If ADEQ and lake managers can work together to fill in the gaps, it may be possible to address algae-related risks more quickly and effectively.

In Arizona, even though there have been no reported human or domestic animal deaths linked to cyanobacteria since 2022, the threat is real. As ADEQ mentions, harmful algal blooms and the toxins they produce are being studied, but much is still unknown. For now, ADEQ’s message is to stay informed and use caution around any water that may look discolored or have an unusual smell, both signs of an algae bloom.

See all the records here.