COLUMBUS (WCMH) — Three dogs in North Carolina died from blue-green algae poisoning after visiting a pond with high toxicity levels.

That same blue-gree algae is also commonly found in Ohio.

Because the algae is so common, workers at Metro Parks keep an eye on waterways so they know when a bloom has happened.

Blue-green algae grows on hot, sunny days and begins to die when the skies are overcast.

The dying algae release toxins into the water and if the toxicity of the water reaches a certain point, it can be harmful to humans and animals.

“Here at Metro Parks, we monitor it in all of our bodies of water that might have human or even dog contact,” said Tim Moloney, executive director of Columbus and Franklin County Metro Parks. “We keep an eye on it. Our staff’s trained and they look for it.”

But even though it can be seen with the naked eye, you won’t know if the water is toxic. Only through testing can it be determined if the water is safe to be in or for animals to drink.

“It’s really, you don’t know until the test happens,” Moloney said.

That’s one reason Moloney has his staff looking and testing the water.

“They need to get out and pay attention,” he said.

If the toxicity level is too high, the parks will close access to the water and post signs explaining the situation.

Metro Parks said it does have one dog pond shut down in a park on the southeast side of the city. There are posting letting people know not to allow their dogs anywhere near the water. Once the toxicity level goes down, the pond will reopen.