Colorado’s shrinking mountain snowpack — at 66 percent of normal statewide Thursday — forced an expanded federal drought designation covering nearly a quarter of the state with stream flows forecast at half of average, setting off a scramble to secure water supplies.

The scarcity spurred calls for storing more water in reservoirs to sustain the state’s growth boom.

“There’s going to be people without water,” especially in Southern Colorado, U.S. Department of Agriculture snow survey supervisor Brian Domonkos said. “It’s going to be a tight year.”

Denver Water officials planned to pull more of the H2O they deliver to 1.4 million metro residents from northern mountains because the upper South Platte River basin snowpack they rely on remains low. They’re seeking federal approval to expand storage by 77,000 acre-feet in Gross Reservoir west of Boulder, a controversial project.

State agencies, including Gov. John Hickenlooper’s staffers, have been monitoring drought impacts and weighing responses with an eye toward tapping federal drought funds. They also may activate a program to ensure sufficient stream flows for protecting imperiled fish.

“We’re very closely monitoring the situation for impacts to make decisions about what we need to do next,” said Colorado Water Conservation Board climate change specialist Taryn Finnessey.

“Water providers are concerned. Those who have more storage are in a better position than those who rely more on direct flows,” she said. “This is something everybody from the agency level up to the governor’s office is closely watching to make sure we are ready to respond.”

Federal snow-survey data showed paltry snowpack statewide and less than 50 percent of median in southern areas.This means less water will flow into streams and rivers as snow melts. Snowpack in the South Platte River basin crucial for Colorado agriculture measured 83 percent of the norm. Snowpack was at 77 percent in the upper Colorado River basin. And snowpack at 57 percent in the Arkansas River basin and 55 percent in the Gunnison River basin was the lowest in 38 years.

Stream and river flows across Colorado likely will diminish to about 50 percent of average, according to federal flow forecasts. While the peak spring runoff flows in the South Platte and Colorado river basins were expected to reach 80 percent of the norm, the federal forecasts indicated flows will be as low as 25 percent of average along the Gunnison and at reservoirs near Durango and Paonia.

Federal drought monitoring officials on Thursday expanded the extreme drought designations in southern Colorado to cover about 24 percent of the state. Counties adjacent to New Mexico now are eligible for federal drought aid. The drought index showed 90 percent of Colorado under abnormally dry conditions with 74 percent of the state designated in moderate to extreme drought.

For metro Denver residents, the low snowpack, about 70 percent of the norm at the south end of Denver Water’s collection system, which holds 90 percent of metro Denver’s water supply, means heavier than usual reliance on runoff water from northern areas, where snowpack is thicker.

That’s not ideal but will help ensure steady water, utility officials said, adding that stream flows this year may not be sufficient to fill reservoirs.

“This year’s imbalance underscores the need to expand Gross Reservoir, which is Denver Water’s major storage reservoir on the north end of our system,” said Denver Water chief executive Jim Lochhead. “The expansion will help to ensure we’re less vulnerable during years like this and better prepared for events like forest fires and infrastructure failures on the south.”

Northern Water officials who supply cities and farmers north of metro Denver were planning to draw down reservoirs, where they have saved up 25 percent more water than usual for this time of year.

“We’re better off than other parts of the state, but our snowpack is still 20 percent below normal,” said Northern Water spokesman Brian Werner. “How much precipitation are we going to get? Spring storms are going to make or break this season for us.”

“We will release water from our storage. That’s why you have storage. This year’s conditions really emphasize the value of storage. Down the road, this state is going to have to have additional storage. And we will have to reuse more water. And there will have to be increased conservation.”

More than 80 percent of the water that Colorado residents divert from streams and rivers is used to irrigate crops. People in urban areas use about 10 percent. The oil and gas industry uses less than half a percent for the hydraulic fracturing that speeds extraction of fossil fuels by injecting water, sand and chemicls underground.

That leaves diminishing water for aquatic life — especially during dry times.

Colorado officials have developed a program with the Colorado Water Trust to purchase water that farmers and cities with rights to water are entitled to divert and then leave that water in streams and rivers. The idea is to release flows from reservoirs strategically to benefit ecosystems when water flows otherwise could disappear.

“We have that option,” the Colorado Water Conservation Board’s Finnessey said. “It keeps more water in the rivers for environmental purposes and water rights holders are compensated. Higher flows help maintain healthy river ecosystems. The endangered fish species in Colorado are always a concern.”

Conservation groups back that effort and on Thursday raised concerns that near-record low snowpack in Colorado will lead to degraded fish habitat and warmer water temperatures.

“Colorado’s legislators and water leaders need to continue to develop tools that allow irrigators and other water users the flexibility to use water in creative ways, including leaving it in streams during dry years like this,” said Trout Unlimited director David Nickum.

“We’ll be depending on these programs more and more,” he said, “as rivers face pressure from growing demands, changing climate and droughts.”

UPDATED: This story was updated at 10:34 a.m. on April 6, 2018, to add context to a quote from U.S. Department of Agriculture snow survey supervisor Brian Domonkos.