Dead fish are stinking up Sloan’s Lake in Denver. Here’s why.

DENVER — Dead fish are not only creating an unsightly experience at one of Denver’s most beautiful parks, but they’re also stinking up the place.

Viewers who contacted Denver7 over the weekend raised the alarm with concerns about the number of dead fish whose carcasses started piling up along sections of Sloan’s Lake.

The foul smell coming off the water as people were recreating this weekend was also an assault on the senses, viewers told Denver7.

So what’s to blame?

“The extreme heat we’ve been having is bringing down oxygen levels,” according to Stephanie Figueroa with Denver Parks and Recreation (DPR), who added that could be a “naturally occurring” factor contributing to the fish die-off at the lake.

There is also “a lot of blue-green algae” in the water at Sloan’s Lake at the moment, which is also contributing to these fish die-offs, she said.

Algae are an important part of aquatic food webs, but lakes with high nutrients are more susceptible to blue-green algae (also called cyanobacteria), which can produce toxins that may cause negative health impacts for humans and pets – and yes, even fish – at elevated concentrations, according to Colorado Parks and Wildlife officials.

Which is why DPR officials are recommending people stay out of the lake, and keep an eye on their pets so they don’t drink water that may contain blue-green algae.

Already this summer, four bodies of water across the state are showing high levels of toxic algae, including Barr and Cherry Creek lakes in the Denver metro.

Looking for signs of blue-green algae in a lake near you? State health officials recommend checking for the following signs to determine in an algal bloom is harmful:

• Resembles thick pea soup or spilled paint on the water.
• Looks discolored — generally green, red, gold, or turquoise but typically not stringy or mustard yellow (the latter is probably pollen).
• Has foam, scum, or algae mats.

What to do you if you or your pet comes into contact with blue-green algae

If your dog gets into a harmful bloom, health officials advise that you rinse your pet off immediately with fresh, clean water. If you, a friend or a family member come contact with the bloom, immediately wash with soap and water.

If your pet has been poisoned by the algae, it’ll show symptoms anywhere from 15 minutes to several days, including diarrhea or vomiting, weakness or staggering, drooling, difficulty breathing and convulsions or seizures, according to health officials.

If your pets are exposed to the water and experience those symptoms, contact your veterinarian immediately, as these toxic algae can kill your pet.

How you can play your part to mitigate toxic algae blooms

While algal blooms are common in the summer when water temperatures rise, there are some things you can do to not make them worse, state health officials say.

Picking up after your pet and properly disposing of their waste prevents nutrients found in excrement (such as nitrogen and phosphorus) from entering waterways, which contribute to algae blooms.

Refraining from using too much fertilizer is also one way in which algal blooms can be kept at bay.

If using de-icers, make sure they don’t contain urea (this information will be on the de-icer bag), health officials said.

To learn more about blue-green algae, head to the CDPHE’s website.