By Stephanie Stahl

PHILADELPHIA (CBS) — There’s a health warning to pet owners across the country about a potentially deadly algae that’s growing in lakes and ponds. The harmful algae blooms can grow in both fresh and marine water, and they aren’t always visible. While it can be harmful to humans, experts say it’s most dangerous to dogs who like to swim.

It’s a summertime menace lurking in the water — a microscopic bacteria called blue-green algae that grows in lakes in warm weather.

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In recent weeks, several dogs have been poisoned by the algae. In Texas, an Australian Shepard died less than an hour after ingesting the toxic algae.

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In Georgia, a border collie suffered the same heartbreaking fate.

The algae releases toxins that can cause liver damage, respiratory paralysis and organ failure, among other deadly conditions.

“The bacteria breaks down in the stomach and digestive acids and rapidly releases a lot of toxins,” veterinarian Dr. Daniel Deciechi said.

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Vets say dogs can also ingest the toxins by licking their fur. Quick action can be life-saving.

“Wash the dog. Step two is get them to a veterinary facility as quickly as you can once you see an onset of signs,” Deciechi said.

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But that didn’t save three dogs who started having seizures after playing in a North Carolina pond. The dogs died five hours later at the vet.

“They just needed to cross that rainbow bridge together, as the trio that they were,” dog owner Denise Mintz said.

There have been a variety of warnings about the algae from health departments in Pennsylvania and New Jersey, but none recently in the Philadelphia area.

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Officials with the Army Corps of Engineers in Philadelphia say the recent heavy rain followed by hot temperatures has caused a spike in the algae. The latest advisory is for Blue Marsh Lake in Berks County.

Stephanie Stahl