The way Virginia responds to Harmful Algal Blooms (HABs) is changing—starting in April 2025, algae toxins, not cell counts, now determine when recreational health advisories are issued. This marks a major shift in how the Virginia Department of Health (VDH) and the Department of Environmental Quality (DEQ) monitor water safety in freshwater lakes and rivers across the state, including popular destinations like Lake Anna.

Since the early 2000s, VDH has issued recreational health advisories when harmful algal blooms were detected, relying on both algae cell counts and toxin levels. These advisories were typically triggered when cyanobacteria (commonly referred to as blue-green algae) reached concentrations of 100,000 cells per milliliter or more. Even in the absence of measurable toxins, these high cell counts often prompted public warnings due to the potential for toxin production.

This conservative approach was designed to err on the side of caution. As a result, many advisories have been issued annually, particularly during the hot summer months when algae growth surges.

In areas like Lake Anna, these advisories have become a seasonal concern, often impacting tourism, real estate, and local business. In 2024, advisories generated anxiety and frequent questions about water safety from both residents and vacationers.

Over the last several years, DEQ and VDH scientists began noticing a pattern. In a review of more than 400 samples collected from across the state between 2020 and 2024, nearly 25% exceeded the cell count threshold, but none of those samples showed toxin levels above the state’s health-based safety limits.

This finding, supported by additional research and consistent with updated guidance from the U.S. Environmental Protection Agency (EPA), revealed a flaw in the old approach: high algae counts do not necessarily indicate the presence of harmful toxins. In fact, many blooms contain little to no detectable toxins.

The previous strategy, while protective, often led to advisories that didn’t reflect actual health risks—causing unnecessary concern and consuming significant resources for monitoring, signage, and public communication.

Under the revised guidance, advisory decisions will now be based on measured toxin concentrations. Specifically, VDH will issue recreational health advisories if any of the following toxin thresholds are exceeded in a water sample: Microcystins: ≥ 8 micrograms per liter (µg/L), Anatoxin-A: ≥ 8 µg/L, Cylindrospermopsin: ≥ 15 µg/L, and Saxitoxin: ≥ 4 µg/L.

For lakefront residents, boaters, and swimmers, the updated policy provides reassurance that advisories are now directly linked to actual health risk. When an advisory is posted, it will mean that toxins have been confirmed at levels known to cause harm—not just that algae is present.

At the same time, the Virginia Department of Health is still urging us to use caution around discolored or foul-smelling water, even if no advisory has been issued. Pets and small children are especially vulnerable to algae toxins, which can cause symptoms ranging from skin irritation to liver damage, neurological issues or worse.

Jen Bailey

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