The Boulder Police Department warned pet owners not to let their dogs into the Boulder Reservoir after fire-retardant slurry was dropped into the St. Vrain Supply Canal, which feeds the reservoir.

Several wildfires are burning in Colorado, including the Alexander Mountain Fire and the Stone Canyon Fire. The Alexander Mountain Fire ignited on Monday and has since grown to surpass 5,000 acres with 0 percent of the fire contained. As of Tuesday night, the Stone Canyon Fire had reached 1,320 acres and also was 0 percent contained.

While responding to the fires, firefighters dropped a fire-retardant slurry into the canal. The slurry is expected to cause some impacts to the nearby Boulder Reservoir. The impact prompted the Boulder Parks and Recreation Department and the Boulder Police Department to issue a warning to pet owners.

"FYI #Boulder Nearby fire response affecting the Boulder Reservoir: Earlier today, while responding to the Stone Canyon wildfire north of Boulder, fire-retardant slurry was dropped into the St. Vrain Supply Canal, which flows into the Boulder Feeder Canal and then into Boulder Reservoir," the Boulder Police Department shared on X, formerly Twitter on Wednesday morning. "As a result, slurry has entered the Boulder Reservoir. The slurry contains a red dye and phosphorus and ammonia-based ingredients, which are not anticipated to pose a threat to human health."

Since the reservoir isn't used as a drinking water source, there's no threat to public health. However, the slurry could impact wildlife and pets depending on its concentration. It could also cause skin and eye irritation if someone were to swim in the impacted waters, depending on concentration levels.

"The slurry may adversely impact aquatic life and wildlife depending on concentrations," the Boulder Police Department said. "We advise against fishing and recommend community members keep their dogs out of the water."

Staff will continue testing the water over the coming days to determine slurry levels.

Several road closures have been announced since the fires started, and mandatory evacuations are ongoing. Evacuations began on Monday and have continued through Tuesday, according to the Larimer County Sheriff's Office, which is managing the evacuations, with the most recent mandatory evacuation order issued for the north side of Carter Lake north to Highway 34 just after 4 p.m. local time on Tuesday. Newsweek reached out to the sheriff's office by email for comment.

Hundreds of local, state and federal personnel are working to combat the flames from both fires. In addition to impacting Boulder Reservoir, officials closed Horsetooth Reservoir to the public so that firefighting personnel could source water from the lake for their efforts.