LARIMER COUNTY, Colo. (CBS4) – An attack is now under way to prevent the damage done by the two recent wildfires from getting worse. It’s a fight to save the reservoir providing drinking water to tens of thousands of people.

The Hewlett Gulch Fire burned in the foothills of Larimer County in May, and that was followed by the much more destructive High Park Fire last month. Now crews are working to prevent mud, debris and ash from getting into Greeley’s drinking water supplies.

Horsetooth Reservoir is just one of many water sources the city of Greeley uses for its city water. Right now crews are working on protecting another reservoir not far from Poudre Canyon from being contaminated after the Hewlett Gulch and High Park fires.

The coordinated attack is to prevent debris from entering the water supply in the Poudre Canyon. On Tuesday two helicopters were making strategic drops of straw around Milton Seaman Reservoir.

“I’ve never seen this reservoir in the peril it’s been in right now as far as the basin being threatened,” said Randy Gustafson, Greeley Water Resource Administrator. ” It will fill up with contaminants; things you wouldn’t be able to dump into the river, so we would lose one of our major reservoirs for the city of Greeley.”

Native grass seed has been planted in the same spots helicopters have been dropping straw.

“What we’re doing here is we’re trying to protect these slopes, give them cover, and that will stop that stuff from coming down into the reservoir,” Gustafson said.

Crews will be working for another week dropping straw on close to 700 acres of charred land.

There are plans to perform the same type of mitigation in the burn areas along the Poudre River.

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