Department of Health officials are warning about a potentially toxic algae that has now been found in seven New Brunswick lakes.

Not all algae blooms are harmful, but blue-green algae can produce toxins that can cause skin, eye and throat irritation upon contact, and more serious health effects, such as severe gastrointestinal illness, if consumed. (CBC File Photo) Washademoak Lake, which is popular among cottagers in the Saint John area, is the latest to be added to a growing list of lakes containing blue-green algae this summer.

The bacterial organisms, also known as cyanobacteria, can produce toxins that can be harmful to human health and fatal to pets and livestock.

Accidentally ingesting the contaminated water while swimming or during other recreational activities can result in headaches, fever, sore throat, dizziness, stomach cramps, nausea, diarrhea and vomiting, officials say. These symptoms can last for several days.

Swimming in water containing the toxin can cause skin, eye and throat irritation.

Children, immuno-compromised individuals and animals are considered most at risk for severe effects.

Fredericton veterinarian Ali Reed has noticed at least five cases of dogs becoming sick after being in one of the affected lakes in the past month.

"If they've been exposed … usually it's when they've been swimming or drinking while they're swimming," Reed said.

"The symptoms can be [central nervous system] symptoms, so neurologic, or rapid liver failure, so it can happen really quickly, usually shortly after they've been swimming. It can be pretty serious, so it's important to seek veterinarian care."

The other lakes currently covered by the public health advisory include:

Grand Lake

Harvey Lake

Chamcook Lake

Lake Utopia

Lac Baker

Lac Unique

Department of Health officials say they don't want to discourage people from enjoying the outdoors, but are advising against swimming, water-skiing and other recreational activities in the affected lakes.

"Even if you can't see a bloom floating on the surface of the water, that doesn't mean one isn't present," its website states.

"Toxins may persist in the water for several weeks," it adds.

They say every body of water affected by the blue-green algae this summer will be monitored for the next two years, to see if the algae blooms come back.