Blue-green algae has been spotted in Loch Lomond (and is potentially within other lochs), and can pose a great threat to pets and livestock.
Blue-green algae can produce toxins that can kill dogs and other animals. In humans it can cause rashes after skin contact and illnesses if swallowed. So if we have posted a warning or if there are warning signs on the Loch shore, then people are advised to keep themselves and their pets and livestock out of the water.
The Pet Poison Helpline classifies its level of toxicity as “generally moderate to severe” and notes that “very small exposures, such a few mouthfuls of algae-contaminated water, may result in fatal poisoning.”
Symptoms include:
  • Diarrhea
  • Vomiting
  • Blood in stool or black, tarry stool
  • Pale mucous membranes
  • Jaundice
  • Abnormal blood clotting
  • Elevated liver enzymes
  • Low blood sugar and protein levels
  • Seizures
  • Disorientation
  • Coma
  • Shock
  • Excessive secretions (salivation, tearing, etc)
  • Neurologic signs (muscle tremors, muscle rigidity, paralysis, etc)
  • Blue discoloration of the skin and mucous membranes
  • Difficulty breathing


Blue green algae can be a problem during the warmer months. The algae blooms can make the water become green, blue-green or greenish brown and several species can produce musty, earthy or grassy odours, and can also cause foaming on the shoreline.

We are often asked to advise when the warning is over. However this is difficult to predict, because blue green algae blooms can form on the water and dissipate again within hours or days, depending on the weather and the water temperature. The blooms normally form in warm still water, so they can form on a still morning around sheltered shore areas, but then get broken up by rain or waves if the wind picks up.

Due to this changeful nature of blue green algae blooms we recommend people err on the side of caution if they know there has been a warning in recent days.

Because of the risk to animals and humans, when we are notified that an algae bloom has been seen in an area of the Park, we post warnings online right away to let people know. We also inform the relevant local authority so they can post warning signs on the shorelines, and report it to SEPA

Loch Lomonds & trossachs National Park

If you believe you have spotted Blue-Green Algae and there are no warning signs present on the shore, please contact the environmental health team at your Local Authority. SEPA can also be contacted.

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