Blue-green algae can be harmful to humans, and lethal to dogs.

Cherry Creek State Park has closed its popular swim area due to naturally occurring algae blooms. 

"The park has closed the swim area due to elevated levels of cyanobacteria (blue-green algae) growth. The swim area will remain closed until tests provide acceptable conditions to re-open," says Colorado Parks and Wildlife (CPW). 

Blue-green algae is the result of a variety of factors, such as warmer temperatures, stagnant waters, and nutrient loading from fertilized lawns. With the temperatures soaring in recent weeks, blooms like these will be more common. They can be toxic, so its best to avoid any water that appears to have clumps of algae of any color floating on the top.

"Some algae blooms produce toxins (poisons) that can cause illness in humans, pets, waterfowl, and other animals that come in contact with the algae. These are called harmful algae blooms (also called HABs or toxic algae)," says the CDPHE.

At Cherry Creek State Park, there are more algae blooms in other areas of the park, and while CPW isn't closing the entire park, it has placed highly visible signs throughout the lake warning users about its presence. According to CPW, the stream in the Dog-Off-Lease-Area has been tested and does not show signs of algae at this time. You can check conditions at Cherry Creek State Park here

The CDPHE recommends the following:

  • Keep kids out
  • No pets in the water
  • Do not drink water
  • Avoid contact with algae

It is important to note that blue-green algae is extremely toxic to dogs, and it can be lethal very quickly. Here are a few precautions to keep your pets safe

  • Do not let pets eat algae, get in the water, or go on the beach or shoreline.
  • Rinse pets off with tap water after they have been in a lake, river, or pond; do not let them lick their fur until they have been rinsed.
  • Seek veterinary care immediately if your pet has consumed or licked algae on its fur after swimming or playing in water that has an algal bloom.

For more information on toxic blue-green algae and tips to avoid it, please read Toxic Blue-Green Algae in Colorado: What it is and How to Avoid it.