On Tuesday, July 30, while responding to the Stone Canyon Fire north of Boulder, fire-retardant slurry (a material used to put out fires) was dropped into the St. Vrain Supply Canal, which flows into the Boulder Feeder Canal and then into Boulder Reservoir. As a result, the slurry has entered the Reservoir.The slurry contains red dye and phosphorus and ammonia-based ingredients, which are not anticipated to harm human health at the estimated current concentrations.

Fire-retardant slurry in Boulder Reservoir currently causing minimal impacts to recreation, none to water quality

On Tuesday, July 30, while responding to the Stone Canyon Fire north of Boulder, fire-retardant slurry (a material used to put out fires) was dropped into the St. Vrain Supply Canal, which flows into the Boulder Feeder Canal and then into Boulder Reservoir. As a result, the slurry has entered the Reservoir.

The slurry contains red dye and phosphorus and ammonia-based ingredients, which are not anticipated to harm human health at the estimated current concentrations. For community awareness:

  • The Boulder Feeder Canal and Reservoir are not currently being used by the City of Boulder as a drinking water source so there is no risk to public health from the city’s drinking water. The Canal and Reservoir are not typically used as a drinking water source for the city.
  • At high concentrations, the slurry may adversely impact aquatic life and wildlife. The city currently does not anticipate impacts at this level.
  • Due to proximity to the canal inlet, the city advises against fishing and recommends Reservoir visitors keep their dogs out of the water on the Reservoir’s North Shore.

City of Boulder staff are testing water quality in the Reservoir to evaluate impacts over the coming days. The volume of slurry is estimated to be less than 0.001% of the total Reservoir volume. At this level of dilution, it is very unlikely to see human health impacts.

City staff are also evaluating water conditions, but don’t anticipate making additional adjustments to recreation operations with lake and swim beach operations continuing as programmed.

When available, additional information will be posted on Boulder Parks and Recreation’s Twitter/X feed, and Facebook and Instagram pages. Community members can also receive immediate operational impacts for Boulder Reservoir by texting “BPRReservoir” to 888777.

Thank you to our community for their understanding and thank you to our firefighters as they work to control wildfires in our community.

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