Blue-Green Algae Tips

Blue-Green Algae Tips for Lake Users

Blue-green algae bloom

Blue-green algae or Cyanobacteria,  is a common and natural component of the microscopic plants (plankton) in Lake Champlain and other waters. Some blue-green algae produce natural toxins or poisons. When the algae die and decompose, toxins can are sometimes released into the water.

Blue-green algae are an ancient group of algae. Although they are most closely related to other bacteria, they can photosynthesize like green plants. Blue-green algae reproduce rapidly in lakes and ponds with adequate amounts of sunlightair/water temperature andnutrients like phosphorus and nitrogen.

Blue-green algae can become very abundant in some sections of Lake Champlain as the water warm in mid-summer. Particular problem areas are Missisquoi Bay and St. Albans Bay. Under calm conditions, the blue-green algae can accumulate in thick layers on the surface or along the shoreline. These accumulations are often referred to as “blooms” or “scums.” Although blue-green algae blooms can create nuisance conditions and undesirable water quality, most blooms are not toxic.

For much of the year, Lake Champlain is safe to swim in, but it is important to be aware of algae blooms. Blue-green algae blooms usually don’t occur until July, and are most common in August and September.


Is Blue-Green Algae Really Dangerous?

While there are no documented cases of human illness due to blue-green algae in Lake Champlain, caution around the algae is urged, especially for pet owners. If animals ingest the toxins, they can become paralyzed and die quickly. The signs of such poisoning include weakness, staggering, difficulty breathing, convulsions and death.

Some blue-green algae produce toxins that could pose a health risk to people and animals when they are exposed to them in large enough quantities. Health effects could occur when surface scums or water containing high levels of blue-green algal toxins are swallowed, through contact with the skin or when airborne droplets containing toxins are inhaled while swimming, bathing or showering.

Recreational contact, such as swimming, and household contact, such as bathing or showering, with water not visibly affected by a blue-green algae bloom is not expected to cause health effects. However, some individuals could be especially sensitive to even low levels of algal toxins and might experience mild symptoms such as skin, eye or throat irritation or allergic reactions.

During the summers of 1999 and 2000 the death of two dogs was attributed to blue-green algae poisoning, after drinking large amounts of contaminated water directly from the lake.

While blue-green algae toxins have been detected at many locations in Lake Champlain, the highest concentrations of toxins are usually found in blooms and shoreline scums. These dense accumulations pose the greatest potential health risks. Watch for dense accumulations of algae and avoid these areas. 


How Does Weather Affect Blue-Green Algae Blooms?

blue-green algae tips

Surface water affected by blue-green algae can be so strongly colored that it can develop a paint-like appearance.



The warmer water temperature results in an increase in the amount of blue-green algae and the presence of blooms.

Weather can also influence where blue-green algae will accumulate. During extended periods of calm and sunny days, blooms can accumulate at the surface in any location. Wind and waves may cause them to form along shorelines or in protected areas. Shifts in wind direction can move a bloom from one location to another.

Periods of cool rainy weather can often lead to the disappearance of a bloom.




Properties of Blue-Green Algae Blooms

  • The water may appear cloudy and look like thick pea soup.
  • Blooms are generally green or blue-green in color, although they sometimes can be brown or purple.
  • A thick mat or foam may form when a bloom washes onto shore.
  • large numbers of dead fish, waterfowl or other animals.
  • sudden, unexplained sickness or death of a cat or dog.
  • a skin rash on humans after being in the water.
  • Not all blue-green algae produce toxins, however there is no way to tell just by looking at them.
  • View this Vermont Dept. of Health photo gallery for what a Blue-green algae bloom looks like


What Can You Do To Avoid Blue-Green Algae?

Boaters, swimmers, water-skiers, waders, parents, pet-owners and residents should become familiar with the appearance of blue-green algae. Everyone should avoid contact with dense accumulations of these algae.

Children are at higher risk because they are more likely to drink the water.

Do not allow pets in algae-contaminated water because they will also drink the water and consume algae on their fur.

If your dog does swim in a bloom, wash the dog off when it comes out of the water; make sure the dog does not lick the algae out of its fur.

If the water has a lot of algae in it, make sure the dog drinks from another source.

If you believe that someone has become ill because of blue-green algae, please contact the VT Department of Health at 800-439-8550 or the NYS Department of Health at 518-402-7820.


How Can You Help Prevent Blue-Green Algae Blooms?

blue-green algae tips

Sometimes blue-green algae becomes so abundant that it forms floating rafts or scums on the surface of the water.

Algae blooms typically occur during sunny, calm weather when high concentrations of nutrients are present in water. The two important nutrients that can cause a bloom are phosphorus and nitrogen, found in animal and human waste and fertilizers.

To help decrease nutrients flowing into streams, ponds and lakes:

  • Don’t use more lawn fertilizers than the recommended amount, and keep fertilizers out of storm drains and off driveways and sidewalks.
  • “Don’t ‘P’ on the lawn!” It’s the Law! New laws in Vermont and New York that took effect January 1, 2012, prohibit the application of phosphorus fertilizers except in certain circumstances.
  • Maintain or plant native plants around shorelines and streams. Native plants don’t require fertilizers and help filter water.
  • Properly care for and maintain your septic system.
  • Do not allow livestock to drink or defecate in streams or lakes. Don’t overfeed waterfowl.
  • Take steps to prevent soil erosion.


* Check the Current Lake Champlain B-G Algae Status Map Here *