Spring and summer "blooms" (rapid increase in concentrations) of a primitive group of organisms, the cyanobacteria (sometimes mistakenly referred to as "blue-green algae"), have been documented in New Hampshire lakes this year, focusing attention on the potential health threats from the toxins they produce.

The N.H. Department of Environmental Services (NHDES) posted beach advisories warning of cyanobacterial contamination in at least 21 lakes so far in 2009--a substantial increase over the 14 advisories posted last year.

Beneficial algae differ from toxin-producing cyanobacteria

Algae occur in all New Hampshire waters, providing oxygen and serving as an important food source that forms the base of the aquatic food chain. Occasional spring, summer and fall "blooms" (rapid increase in concentrations) of algae have been known to occur but are historically rare on all but a small percentage of New Hampshire lakes. It is also common during sunny, quiet summers to see cotton-candy-like green to almost white "clouds" of green filamentous algae floating in the shallows of the many lakes with aquatic plant beds.

But cyanobacteria, which used to be called "blue-green algae," produce a range of compounds toxic to humans, pets and wildlife. When present in large-enough concentrations, as are found typically during bloom events and when the surface populations are concentrated due to wind and water currents, toxin concentrations can reach levels of concern.

Potential human health effects from exposure to cyanotoxins

Long-term exposure to these toxins is suspected to cause chronic symptoms and ingestion of the toxins over long periods may possibly damage the liver, kidney and nervous system.

Short-term exposure to cyanotoxins through activities such as swimming and boating in cyanobacteria-contaminated water or showering in water drawn directly from contaminated lakes, may produce symptoms such as skin rashes, muscle pain, eye and ear inflammation or infection, nausea, disorientation, diarrhea and flu-like symptoms.

Cyanobacteria don't always produce significant quantities of toxin capable of producing symptoms like those described above. Only five of the common cyanobacteria in New Hampshire waters have been shown to produce at least one toxin.

Stay vigilant

While there have been no documented cases of negative human health effects from cyanotoxin exposure in New Hampshire, it is best to be vigilant and cautious. Keep pets and children (who are at greatest risk) away from any surface scums, "blooms" or underwater "mats" that are green, yellow-green or bluish green.

Other states have reported dog illnesses and deaths from cyanotoxins when dogs drank small volumes of heavily-contaminated water or licked contaminated water from their coats.

Everyone should heed the posted warning signs and keep aware of cyanobacteria beach advisories by checking the NHDES beach program Web site.

Current advisories are posted based on the amount of potentially toxin-producing cyanobacteria, rather than on any measured amount of toxins.

Researchers are currently investigating additional methods to predict toxin concentrations, but as any cyanobacteria bloom may produce more than one toxin and not all toxins are easily and quickly identified, the microscopic analysis, as is done for the advisories, is still the best option.

Learn more

NHDES Beach Program Lots of information on cyanobacteria, current beach advisories, and presentations from recent informational workshops.

NH Lakes Association Information on algal and cyanobacteria blooms.

UNH biotoxins lab Ongoing research to understand the role of biotoxins in aquatic systems and their importance as a threat to public health and water quality.

Cyanobacteria under the microscope Click on fourth picture down in the far right column.

Cyanotoxins and the health of domestic animals and humans Presentation by Dr. Jim Haney of the UNH Center for Freshwater Biology.