From dog fatalities in New Brunswick to lake closures and warnings in Nova Scotia, much of the Maritimes have been affected by recent blue-green algae blooms.

The tiny aquatic plants live in fresh water and pose a threat to both pets and people.

A popular off-leash dog area in a Halifax park is closed after blue-green algae was spotted in Lake Micmac last week.

Signs are posted at the entrances to Dartmouth's Shubie park after a resident reported a blue-green algae bloom in the nearby lake.

Pet owners are taking note of the warnings.

“Yeah, you can't really let them go in, right because you don't want them to get sick,” said Carol Anne Cox.

John MacDonald also walks his dog there.

“She's been coming here almost every day for nine years, since she was a puppy, and she likes to run, chase her ball and swim through the water, but you don't dare put her in with this stuff you know, what happened in New Brunswick,” he said.

In New Brunswick, three dogs died after swimming in the St. John River. The deaths were caused by blue-green algae in the water and there are now warning signs in the Fredericton area, too.

The algae are microscopic aquatic plants that multiply rapidly in summer, leading to a bloom.

“The trouble with blue-green algae is that that is a group of bacteria that sometimes produces toxins and these are toxins that can be particularly harmful,” said Cameron Deacoff, an environmental protection officer with Halifax Regional Municipality.

Those toxins have serious effects. If they come into contact with skin, they can cause rashes and swelling. If ingested, they can cause headaches, fever, or even liver damage.

And they're fatal for small animals like dogs.

The bloom in Lake Micmac means this off-leash dog area is closed for swimming to people and their dogs, and while the water looks fine, the bloom, isn't far away.

It starts at the shoreline and extends out about three to five metres, said Deacoff, who’s not exactly sure why the blooms have formed there.

“They may occur due to a variety of conditions that are really hard to predict,” he said.

The recent heat, the amount of daylight, and excess phosphorus in the water can all contribute the growth of the bacteria.

The algae bloom in Lake Micmac is just a short walking distance away from the beach. The city will now do tests at both sites to see where toxins are being released.

Several samples were taken Wednesday and more will be taken later in the week. Results from those tests should be in before the weekend.

Deacoff says residents can help by keeping the nutrients feeding the bacteria out of the water in the first place.

“If you're putting fertilizer in the garden, if you've got a dog and it does its business, dispose of it properly, all that kind of stuff,” he said.

When it comes to finding a cool place to get relief from the heat. it's best to stay out of the water in affected areas until further notice.

Officials in the Maritimes where blue-green algae blooms have been spotted are keeping an eye on things. In Halifax there is more testing to be done before they can decide if this area in particular will be reopened to swimming for both people and their pets.

With files from CTV Atlantic's Heidi Petracek.