Harmful Algal Blooms (HABs): Identifying Risks and Taking Precautions
2020 Summerby Hannah Riedl and Adam Sigler
Hannah Riedl works in the Watershed Protection Section of the Montana DEQ and Adam Sigler is the MSU Extension Water Quality Specialist.
Algae is a term often casually used to describe anything green that is growing in water. Some green growth in waterbodies is natural and necessary because it feeds insects that feed fish. When algae growth accelerates however, it causes an “algal bloom.” Cyanobacteria are a specific type of algae that can release cyanotoxins (toxins), which are the concern associated with Harmful Algal Blooms (HABs). HABs can cause illness in people and even death in pets and livestock. HABs occur every year in Montana, so it is important to understand how to identify a potential HAB and avoid risks.
Harmful algal blooms are caused by cyanobacteria, also known as blue-green algae; HABs are not caused by green algae (see sidebar for differentiation). HABs are most commonly observed along the windward side of standing water (lakes, reservoirs, ponds, etc.), often washing up along shorelines. Less frequently, they may also occur in slow-moving eddies or side-channels of streams and rivers. While it is feasible that cyanobacteria or their toxins could travel downstream from lakes and reservoirs, flowing water is not considered at high risk for HABs.
When cyanobacteria are present in a waterbody, there is a risk cyanotoxins will be released. Unfortunately, predicting when cyanobacteria will release toxins is not easy. For this reason, the best practice is to STAY OUT IF IN DOUBT. When a suspected HAB is present, keep children, pets, and livestock away from the water so they cannot contact or consume the cyanobacteria and possible cyanotoxins.
Generally, the highest health risks associated with HABs come from consuming water with toxins present or from entering the water. However, indirect exposure from splashing or aerosolized water containing toxins can also affect boaters, fishermen, and shoreline users. Boiling is not effective at removing toxins for safe drinking, may concentrate the toxins in the remaining water, and may introduce toxins into the air. There is not enough information to know if cyanotoxins are a concern with consumption of fish, but it is recommended to rinse the skin with clean water prior to filleting and remove the organs prior to cooking.
If exposed to a potential HAB and symptoms occur, shower immediately and contact a doctor or veterinarian. In humans and animals, symptoms may include: skin, ear, eye, nose, or throat irritation; respiratory issues; lethargy, paralysis, tremors or seizures; abdominal pain, diarrhea,
or vomiting.
Knowledge about HABs and ability to differentiate cyanobacteria blooms from green algae will empower you to avoid exposure or respond appropriately if exposed, including providing information to a doctor or veterinarian if needed. Imagine returning from a walk to a local pond with your child and/or your dog. A rash appears on your child’s legs or the dog is acting lethargic. Did you notice algae growth in the pond? If so, did it look like cyanobacteria or was it green algae? If it looked like cyanobacteria, maybe you instead kept the child and dog out of the water, so exposure to cyanotoxins is not a possible explanation for the symptoms. Maybe the child got into stinging nettle or poison ivy or maybe the dog got into an animal carcass or trash. In an alternative scenario, maybe the child or dog got into the water before you noticed the algae, but you took notice and identified it as possible cyanobacteria; now you know that cyanotoxins are a possible explanation and you can provide information to the doctor or veterinarian.
A few Montana waterbodies that commonly experience cyanobacteria blooms include Beaver Creek Reservoir and Bearpaw Lake (Hill County), Hauser and Canyon Ferry reservoirs (Lewis and Clark County), Clark Canyon Reservoir (Beaverhead County), Hebgen Reservoir (Gallatin County), and Cooney Reservoir (Carbon County). To view a map of past and recent citizen reports, check out the State HAB Program’s webpage: hab.mt.gov. This webpage also has a link to submit citizen reports of potential HABs. The State HAB Program will evaluate report photos and contact you with a visual assessment of potential cyanobacteria presence. If cyanobacteria are visually confirmed, the State HAB program will contact local water managers or public health officials to distribute monitoring resources and recommend advisories as needed.
Limiting nutrient loads to waterbodies and lowering water temperatures can reduce the risk of algae blooms, which in turn reduces the risk of HABs. Vegetation along waterbodies can increase shade and help lower nutrient loads from residential development, fertilizer application, and livestock waste. During warm summer months when algae growth is common, much of the nutrients entering streams come from groundwater. Proper maintenance of septic systems and best practices for fertilizer application are important actions for healthy groundwater and to limit algae growth.
In summary, all Montanans can help manage HABs by becoming educated on how to identify them; by reporting them to the hab.mt.gov website if observed; and by taking steps to reduce nutrient inputs into rivers, lakes, and streams. Always remember, when in doubt, stay out.
For additional information:
• The state of Montana Harmful Algal Bloom website: hab.mt.gov
• Avoiding Algae Issues in Stock Ponds: https://apps.msuextension.org/magazine/articles/5460
• Why pump your septic tank?: https://apps.msuextension.org/magazine/articles/1350