HARTSEL • The Antero Reservoir isn’t empty yet. But it will be in about six weeks.

Facing historically low runoff from this year’s drought-stricken snowpack, Denver Water expects to drain Antero Reservoir within the next six weeks to reduce evaporation losses and preserve water supplies.

On May 1, Denver Water began releasing water from the reservoir, which is located 110 miles southwest of Denver. The move is expected to save roughly 5,000 acre-feet. That accounts for about a quarter of the reservoir’s capacity.

An acre-foot of water is enough to cover an acre of land with one foot of water — or 325,853.3 gallons. That’s more than four times the amount of water used annually by a typical four-person household in Denver, which uses about 70,000 gallons a year.

“Given the severe drought conditions we really need every single drop,” Nathan Elder, manager of water supply with Denver Water, said.

The reason?

In short, this year’s snowpack has been abysmal. In a typical year, the reservoir receives about 13,700-acre feet of water.

“This year we’re expecting 500-acre feet of inflow,” Elder said. “It would be the lowest we’ve ever seen.”

The last time the reservoir was drained to conserve water was 2002.

It took four years for the reservoir to fill, Elder said.

This drought, Elder emphasized, is worse.

While the reservoir would be closed to recreation for the season, it’s unclear when it will reopen.

“The reservoir would need to return to a depth of about 18 feet – roughly 80% of capacity – before Denver Water would reopen for recreation,” officials said.

The water is being moved to the Cheesman Reservoir in Pike National Forest about 65 miles southwest of Denver.

Antero Reservoir has a capacity of roughly 20,000 acre-feet, while Cheesman Reservoir can hold nearly 80,000 acre-feet.

Despite holding less water, Antero loses a far greater share to evaporation because it is shallow — averaging about eight feet deep — and spreads across a broad surface area exposed to the sun and wind. Cheesman, by comparison, reaches depths of about 200 feet, allowing it to store more water with less surface exposure.

Jimmy Luthye, a Denver Water spokesperson, did not know how many visitors Antero Reservoir gets annually.

The impacts of the closure are expected to ripple through one of South Park’s more popular recreation areas.

Known for trophy-sized rainbow, brown and cutthroat trout, Antero draws anglers, boaters and campers from across Colorado.

Colorado Parks and Wildlife recently lifted fishing license requirements as part of an emergency public fish salvage. Additional salvage operations are planned, though the state agency declined to provide details.

Mountain snowpack acts as a natural reservoir that supplies water to Colorado and other Western states as it melts. The snowpack this season peaked and melted early.

This year’s snowpack ranks among the worst on record, heightening concerns about water supplies across the state and the Colorado River Basin, which serves 40 million people in seven states.

Water managers across the Front Range — Arvada, Aurora, Boulder, Denver, Golden and Thornton — have all declared drought restrictions to preserve water levels and, hopefully, avoid stricter measures later this summer when demand naturally increases.

While Elder does not anticipate this year moving into Stage 2 restrictions, which would restrict outdoor watering, next April is a strong possibility — if conditions do not improve.

Elder’s message to the public is straightforward:

“We really need your help to save water this year,” he said. “This is the worst drought that we’ve seen.”