PORTLAND, Ore. (KOIN) — Many people tend to head to the lake or river to cool off when sizzling weather sets in. But the Oregon Health Authority is warning people that harmful toxins can bloom in these bodies of water when temperatures heat up.

All freshwater contains cyanobacteria which is usually harmless. However, it can be dangerous if it grows into a bloom that produces cyanotoxins which can make both people and animals sick when swallowed or breathed in.

Exposure to cyanotoxins can lead to diarrhea, cramps, vomiting, numbness, dizziness and fainting. Someone that is only exposed to cyanotoxins through skin contact and not ingestion can develop a red, raised rash.

Extra precautions should be taken for children and pets whose size and activity levels health officials say make them more sensitive to illness. Animals can get extremely sick or even die just minutes after ingesting cyanotoxins whether by drinking water, licking their fur or eating the toxins from floating mats or on the shore.

Few bodies of water are monitored for cyanotoxins in Oregon, so OHA asks that people inspect the water before jumping in. Should the water be foamy, scummy, thick or have brownish-red mats, health officials say people should avoid it altogether.

“Certain blooms grow on or near the bottom of water bodies like lakes and rivers. While some of them make and release toxins into the water, they don’t change how the surface of the water looks, making them hard to see,” said OHA.

To see if an advisory has been issued for a lake or river, visit OHA’s website here.

Although people should avoid the water if a bloom is present, health officials say it’s still safe to enjoy nearby out-of-water activities like camping, hiking or biking.