Not only does it form the basis of the aquatic food web, algae have the power to put a lid on bovine burps. Algae can also be made into a substitute for fossil fuels, and is a heathy and tasty food supplement for humans. But from mid-summer through early fall, certain algae can spread toxins through freshwater lakes and rivers, posing a risk to people, pets, fish, and more. Be on the lookout in northern New York State this summer for harmful algal blooms (HABs).

The term algae itself has no strict definition. It may refer to any number of photosynthetic organisms, many of which are not even closely related. Everything from single-cell microbes to giant kelp measuring 150 feet long can be labeled as algae. Worldwide, there are more than 5,000 species of algae, and nearly all of them are beneficial.

As an example, research ongoing since 2017 at the University of California at Davis concluded that feeding a small amount of marine algae to cattle reduced their burps, a.k.a. methane emissions, by 99%. That may seem like a useless piece of trivia, but according to the UN Food and Agriculture Organization, cattle contribute more to global warming than all forms of transportation combined, because methane (CH4) is twenty-three times more potent as a greenhouse gas than carbon dioxide (CO2). Needless to say, algae may turn out to be one of our strongest allies in the fight against climate change.

For more than a decade, the US Department of Energy (DOE) has been researching single-cell algae as a fuel, calling it “one of the fuel sources of the future.” Even though it is not yet a profitable endeavor, several private companies such as Florida-based Algenol and Sapphire Energy of California are now producing algal-based fuels. A DOE website adds that “since it [algae] takes CO2 out of the atmosphere, it is a nearly carbon-neutral fuel source.” Not bad for pond scum.

Freshwater algal blooms differ from those in marine environments, such as the infamous “red tides” that bring potent neurotoxins. When folks report an algal bloom in our neck of the woods, they are talking about cyanobacteria, often called blue-green algae even though it can appear brown or reddish (never mind that most biologists do not recognize cyanobacteria as true algae). While not as dangerous as marine algal blooms, freshwater harmful algal blooms still pose a risk. The New York State Department of Environmental Conservation (NYSDEC) emphasizes that because there is no good way to tell a HAB from a benign one, people should avoid swimming in areas with visible algae, and keep pets out of such waters and off the beach as well.

The problem is that blue-green algae secrete microcystin, a toxic substance which in humans can cause rashes, vomiting, diarrhea, and in a few individuals, a life-threatening reaction. Dogs are particularly vulnerable to HAB poisoning because they may pick up objects on the beach which have come in contact with harmful algae. Symptoms of canine microcystin exposure include unsteadiness, seizures, or difficulty breathing. An exposed dog should be seen by a veterinarian immediately.

HABs can also threaten drinking-water supplies. The US Environmental Protection Agency (US EPA) states that “Toxins from harmful algal blooms are increasingly contaminating source waters, as well as the drinking-water treatment facilities that the source waters supply.” In August 2014, dangerously high levels of microcystin forced the City of Toledo to issue a “Do Not Drink” order to more than 400,000 residents, leaving them without water for three days. The Ohio Health Department advised residents not to even brush their teeth with water from the faucet. The problem was a small HAB near the city’s intake pipes in Lake Erie.

Harmful algal blooms seem to be occurring more often than they did historically. One reason is that water bodies tend to be warmer: summers are hotter than in the past, and the temperate season is longer than it used to be. A NYSDEC web page says HABs “are likely triggered by a combination of conditions that may include excess nutrients (phosphorus and nitrogen), low-water or low-flow conditions, and warm temperatures.” As you enjoy the great outdoors this summer and fall, please report any suspected harmful algal blooms to the NYS Department of Health at harmfulalgae@health.ny.gov  or contact your local health department.

Paul J. Hetzler is a former Cornell Cooperative Extension educator.