Most of the growth is harmless, but some can produce toxic chemicals that cause sickness in people and pets.

When you picture perfect swimming and boating conditions, you're most likely not envisioning the water you see pictured here. Blue-green algae growth, known as cyanobacteria, is made up of microscopic organisms that naturally occur in streams and lakes.

As pointed out earlier, it's more than likely to be harmless, but on the off-chance that it isn't, you don't want to be the dude cannon-balling into the middle of a bloom.

U.S. News:

The Illinois Environmental Protection Agency and Department of Public Health are reminding people to avoid contact with water that looks like spilled green or blue-green paint, has green-color streaks or greenish globs suspended in the water below the service. They also recommend not allowing pets to drink the water.

If there's contact, public health officials recommend rinsing off with fresh clean water as soon as possible.