The Hippo


Jul 22, 2019








Beach trip tips
How to navigate lake warnings

By Ryan Lessard

 “ADVISORY. High levels of bacteria have been detected in this water.” If you see a yellow sign with those words at your local swimming spot, it means the state Department of Environmental Services wants you to know there’s a risk of getting sick. But not all bacteria threats are the same.

So far this month, there have been three cyanobacteria warnings in the state. According to the Current Beach Advisories map on the DES website, there are 10 advisories as of press time, two of which are for cyanobacteria. 
Those are at Silver Lake in Hollis and Elm Brook Park Beach in Hopkinton. Earlier this month, Goose Pond in Canaan also had a cyanobacteria warning, but that has since been lifted, according to Dave Neils, the chief water pollution biologist at DES.
“We’ve actually had documented blooms at about eight lakes and citizen reports at about four different ones,” Neils said.
Cyanobacteria warnings are different from other kinds of bacteria warnings because cyanobacteria blooms are caused by different things and can pose more long-term health threats. 
Neils said cyanobacteria, once referred to as blue-green algae, are photosynthetic organisms that are classified as bacteria and can carry a number of harmful toxins. The two most common strains, or taxa, in the state are called microcystis and anabaena. 
“They’re very unique organisms in that they can produce multiple toxins,” Neils said.
Because they behave like plankton and use sunlight to synthesize food, cyanobacteria blooms occur in response to a number of environmental factors. While the full combination of factors is still difficult to monitor and predict, generally blooms occur after heavy rains that are followed by a stretch of hot, sunny weather.
“That allows for the bacteria to grow much faster … and they have this perfect bloom condition,” Neils said.
Blooms often appear as surface slime or a hazy cloud.
“To the layperson it presents itself as a scum on the surface of the water. It has a very bright green sheen to it, sometimes bluish green. Other times it can be suspended in the water column,” Neils said.
Unlike other bacterial loads, cyanobacteria threats can change rapidly.
“The cyanobacteria bloom can be there one day and it can be gone the next,” Neils said. “Almost overnight the blooms can go away.”
This happens because cyanobacteria control their position in the water with tiny gas vacuoles. As the ideal conditions for blooms disappear, they release the gas and sink to the bottom of the lake.
For lakes where cyanobacteria is actively blooming, humans and animals can become ill through ingestion but also skin contact and inhaling an aerosolized form of the bacteria, according to Neils.
Among the toxins that cyanobacteria produce are some neurotoxins.
“There can be very severe short-term health effects if you have one of these neurotoxins that you ingest,” Neils said.
There have been reports in other states of pets dying from drinking water with heavy blooms or licking themselves after swimming in such water. There have been no reports of humans or animals dying in New Hampshire from cyanobacteria so far, Neils said.
Cyanobacteria can also cause long-term nerve and liver damage. There’s also some new research that’s found a correlation between areas with frequent cyanobacterial blooms and the neurodegenerative disease ALS. But Neils said there’s more research needed to prove a causal link.
E. coli
Unlike cyanobacteria, which behave like a plant with bug-like properties, E. coli is a bacterial species that is not native to water bodies. Rather, it is native to the gastrointestinal tract of warm-blooded mammals, which means if you can find it in a lake, it probably came from feces.
But when warnings are issued and lakes are closed due to high E. coli levels, public health officials aren’t primarily concerned with the E. coli itself. 
“We use E. coli as an indicator organism,” Manchester Public Health Director Tim Soucy said.
In other words, if there’s a lot of E. coli in a lake, it likely means there are other pathogenic microorganisms in there with it, such as salmonella or shigella.
In fact, the E. coli they are finding in water samples is not the same bacterial strain that food safety inspectors recall beef products for.
Similar to cyanobacteria, its prevalence can be affected by rain and temperature, but mostly by runoff. It can also be affected by the presence of geese, dogs, babies in diapers and lots of swimmers. 
“Anything that can put feces in the water is a potential source of E. coli,” Soucy said.
The main pathway for people to become ill from E. coli is oral ingestion of the water. 
Humans can suffer short-term effects similar to those caused by fecal bacteria such as gastroenteritis, nausea, vomiting. 
For the most part, swimmers are given the choice to swim at their own risk when advisories are posted, but in some cases, like with Crystal Lake in Manchester, which is licensed to the city, authorities will enforce the lake’s closure until bacteria levels drop back down to safe levels.

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