Blue Green Algae Blooms

Blue-green algae can form harmful blooms in lakes, ponds, and rivers that make the water murky, and can sometimes make the water look like pea soup or paint. The bloom appears as a yellow or green-colored bloom with floating scum in some areas. The 2015 bloom in White Pond appeared as an extensive emerald (blue/green) and a mustard yellow-colored floating scum.

Blue-green algae blooms can produce toxins that can make pets and people sick. Toxins may be present within the algae cells or in the water.
  • For humans, the primary concern is ingestion of water containing blue-green algae while swimming. Of secondary concern is direct skin contact with the blue-green algae and inhalation of water droplets containing blue-green algae or toxins.
  • For pets, the primary concern is the ingestion of water containing blue-green algae or scum that has washed ashore or gotten onto their skin or fur.
Contact can cause skin and eye irritation, and inhalation can cause respiratory irritation and exacerbate pre-existing respiratory conditions. Toxins are not absorbed through the skin. Ingestion of blue-green algae can cause acute gastrointestinal symptoms, such as vomiting and diarrhea. If the blue-green algae are producing toxin(s), the health effects can be more serious, especially for small pets due to their smaller body weights. Ingestion of the toxins can cause acute gastrointestinal distress and, depending on the specific toxin, can affect the functioning of the liver, kidneys, and/or neurological systems and in severe cases can result in death.

Blue green algae blooms may produce toxins that can make pets and people sick. 
The Concord Board of Health advises:
  • Do not swim
  • People and pets should avoid contact in areas of algae concentration, even on shore
  • Do not allow your pet to swim in or drink the water
  • Do not swallow water and be sure to rinse off after contact

Pet Safety

Call your vet immediately if your pet has been around an algae bloom and shows symptoms such as vomiting, staggering, drooling, or convulsions. These symptoms present themselves fairly quickly after exposure. Animals of most concern are dogs. They have been known to eat the scum that washes ashore and/or lick scum out of their fur. In Massachusetts and in many other states, canine fatalities have been documented due to the ingestion of harmful algae. Learn additional details on additional safety precautions by viewing the Protecting Pets from Algae Blooms (PDF).

When are water advisories lifted?

Algae blooms may last for weeks in the summer, or may disappear quite quickly. Town staff will regularly observe White Pond for the presence of a visible algae bloom and will sample the water as needed to determine if a recreational water use advisory should be issued. MDPH recommends that the recreational water advisory not be lifted until 2 consecutive weekly samples show algal cell counts below the safe limit of 70,000 cells/milliliter of water, or until two weeks after the bloom has faded.