Are algae impacts on Manatee County’s drinking water supply here to stay? What to know

Manatee County officials say they will now conduct regular testing for toxins until a bloom of blue-green algae in the county’s main supply of drinking water subsides after a test recently revealed a trace level of one toxin.

The bloom in the Lake Manatee Reservoir is producing a non-toxic compound called geosmin that is causing a musty smell and taste in residents’ water. Some species of blue-green algae can also produce potent toxins.

County officials previously said that based on the behavior of past blooms in the reservoir, they did not believe the current bloom would produce toxins.

But after concern from citizens and pressure from a water quality advocacy group, the county had the water tested by an independent lab.

The test revealed pre-treatment water from the Lake Manatee Reservoir was at safe drinking levels. Three of the four toxins tested for were not found. A fourth, called saxitoxin, was observed at a trace level of 0.1 micrograms per liter.

That is well below the threshold of 3 micrograms per liter that the World Health Organization defines as a health risk in drinking water.

But toxicity levels can change as a bloom develops.

Blue-green algae toxins are not federally regulated in the U.S., and while some states choose to regulate them, Florida does not. That leaves it up to local water facilities to choose how they monitor for the toxins.

The WHO says the limited data available on saxitoxins in drinking water suggests that they can “be effectively removed by typical drinking-water treatment processes.”

Saxitoxins are the same toxins responsible for most paralytic shellfish poisoning. They can cause temporary neurological and gastrointestinal symptoms.

While extreme cases of toxic shellfish poisoning can result in death, the WHO says that “exposure to a dose high enough to cause severe symptoms is unlikely from ingesting drinking water, based on the currently available data.”

Keep algae monitored, experts and advocates say

Dail Laughinghouse, a professor of phycology (the study of algae) at the University of Florida who has studied blue-green algae for 20 years, said that toxin levels below WHO guidelines in pre-treatment water should not be a cause for concern.

However, he recommended that officials monitor toxin levels as long as the bloom continues.

“Toxin production changes. It can increase or decrease depending on several factors. I would say to keep it monitored. If the toxin concentration is lower than what the guidelines are saying, then they’re doing it correctly,” Laughinghouse said.

After the county announced the test results last week, Suncoast Waterkeeper commended officials for going above what is currently required by law to ensure the safety of drinking water. But the group also called for continued testing.

“The report indicates, however, that trace amounts of saxitoxin were detected,” Suncoast Waterkeeper executive director Abbey Tyrna said in an email. “This means that the algae in the lake can and do produce a potent toxin. Thus, if the bloom intensifies, we can no longer assume that the water is safe to drink. The water must be retested with changing conditions to ensure that the water remains safe to drink. This assurance does not cost the county much and is both reasonable and affordable.”

In an email on Wednesday, the county confirmed that it plans to continue testing the water while the bloom lasts.

“Considering the high amount of algae enumerated during this bloom, this trace level of saxitoxin does not raise alarm,” the county said. “However, it does indicate that the algae are capable of producing the toxin. We will continue to monitor for algal toxins until the bloom subsides.”

The county said additional water samples are being sent to GreenWater Laboratories for testing, and county staff are also using field strips to test for some algae toxins on site.

The county has identified the algae causing the taste and odor issues as Dolichospermum circinale.

The Florida Department of Environmental Protection also took a sample at Lake Manatee on July 25. A state report noted the presence of dead insects on the surface of the water and another type of blue-green algae, Microcystis aeruginosa, present in the lake, but no toxins were detected.

Are blue-green algae issues here to stay?

Laughinghouse, who is studying what triggers blue-green algae blooms and how they can be better managed, says that climate change could make future blooms more frequent, intense or unpredictable.

“Cyanobacteria are common in ponds and drinking water sources. You cannot have healthy water without them. The problem is when they overgrow and sometimes produce toxins,” Laughinghouse said. “And blooms like it hot.”

More algae does not necessarily mean more toxin, Laughinghouse said. Unlike red tide blooms, where higher cell counts mean higher toxin levels, blue-green algae toxicity is highly variable. Laughinghouse said some data suggests that certain blue-green algae species may even produce less toxin as the water gets warmer.

But climate change can introduce a multitude of new factors that make it best to be prepared.

For instance, Laughinghouse said, increased heat could stress organisms in a marine ecosystem and make them more sensitive to a toxin than they would be otherwise.

“Even though the future is blue-green, we can be happy to know that our knowledge about the issue is growing and we’re developing new technology,” Laughinghouse said.

The emerging tech includes new molecular testing methods, plus physical probes and floating platforms that can be used to measure changing water conditions, Laughinghouse said.

Currently, he said local water utilities often do not have enough resources to test for a growing number of issues in drinking water, from blue-green algae toxins to PFAS contamination.

“I think dollars should be spent for monitoring our waters,” Laughinghouse said. “Both for cyanotoxins and other compounds that are public health risks.”

Laughinghouse said state legislators also have the option to establish regulations for toxin levels in drinking water.

“Harmful algal blooms are a bipartisan issue,” he said.

Residents that want to be extra cautious can filter drinking water again at home, Laughinghouse said.

“Activated charcoal will remove most of these compounds. Especially if you’re having geosmin, some of the at-home systems can help with that taste.”

What to know about blue-green algae in Lake Manatee Reservoir

We asked county water officials for some more background on Lake Manatee’s blue-green algae bloom. Here’s what they said.

Has this happened before?

Blue-green algae blooms have been a regular occurrence in Lake Manatee since 1967. Weather conditions dictate that some years are worse than others, but the County typically has to treat for taste and odor seasonally most years. We would expect these issues to continue in the future.

Are the county’s water facilities capable of filtering out saxitoxin and other cyanotoxins if they became present at elevated levels?

The powdered activated carbon being utilized for taste and odor compounds as well as our conventional surface water treatment process have the ability to remove algal toxins. Testing would need to be done to fully determine the level of removal our processes can achieve.

How much does it cost the county to have a cyanotoxin test conducted, and is it feasible to have the water regularly tested during a bloom?

We paid $1,550 for GreenWater to analyze the first samples. This was for two samples and with a 2x mark-up for rush results. It is feasible to have more regular testing done when needed.

Is the county prepared to increase monitoring and testing efforts if blue-green algae blooms become more frequent or severe in coming years, as some scientists predict?

Yes. The County has a long-standing algae monitoring program which includes prevention efforts, algae enumeration and identification and analysis for taste and odor compounds and algal toxins. The algal toxin testing program is where we have the most room for expansion since we have not fully developed our in-house testing methods and rely on contracting out most of that work. Additional staff to fully devote to toxin analysis was included in this year’s budget request for our laboratory.