Editor’s note: This story has clarified the minimum power pool reference from original publication.

This past week, the U.S. Bureau of Reclamation posted an attention-grabbing statistic. By dropping to less than 25% of its capacity, Blue Mesa Reservoir has lost its status as the state’s largest body of water. Lake Granby, itself just 62% full, now holds the title.

The ruins of Iola, a community flooded in the creation of Blue Mesa, are now visible. Parts of the Gunnison River snake through the lakebed in imitation of its historic path before the reservoir was dammed in the 1960s.

Virginia Walton, a volunteer at the Gunnison Pioneer Museum, said she drove by the reservoir this week on her way back from Montrose.

“You could absolutely see the river, and you could kind of imagine what it was like before,” she said.

Colorado’s reservoirs are bellwethers for drought. In a complex system of storing and releasing water, reservoirs like Blue Mesa play a key role in providing access to water and power in the Colorado River Basin, which serves over 40 million people.

In a different year, the water storage unit that includes Blue Mesa might have helped replenish Lake Powell, the second-largest reservoir in the U.S., which now sits worryingly close to minimum power pool.

Minimum power pool is the threshold when water levels drop too low to produce hydroelectric power.

There’s no chance of Blue Mesa contributing much to Lake Powell this year, said Steve Pope, manager of the Uncompahgre Valley Water Users Association.

“If there’s no water here, there’s really nothing you can do with it,” he said.

The Uncompahgre Valley Water Users Association relies on water stored in the Blue Mesa, which is diverted downstream through the Gunnison Tunnel to irrigate tens of thousands of acres of farmland. The communities of Montrose, Delta and Olathe also rely on raw water from the tunnel for municipal use.

The association typically has a secondary water supply from the Uncompahgre River, but Pope said that source is “nonexistent” this year. In anticipation of shortages, the association already limited users to 50% of their allocations this spring.

Pope said he hoped no further restrictions would be necessary before Labor Day. Large row crop producers have already fallowed 30%-60% of their land in the valley, he said.

“We flat out said this was all the water we were going to be able to deliver,” he said.

One bad year compounds risk in the next. If the Uncompahgre Valley users run out of water before spring runoff, the association might have to put out a river call, which could cut off less senior water users from their rights.

The Bureau of Reclamation has taken steps to avoid that scenario, said Caleb Foy, senior water resources engineer at the Colorado River Water Conservation District.

Water managers were already anticipating a historically dry year this spring, when the window for the mountains to accumulate snowpack passed leaving the lowest amount ever recorded. Snowpack melts in spring to produce runoff, which feeds the Colorado River Basin.

If the Bureau of Reclamation and water rights holders along the Gunnison River had not put restrictions in place, Blue Mesa might have been on a trajectory to drain past power pool, Foy said. The reservoir’s generators have an 86.4-megawatt capacity, enough to generate power for about 3,400 homes.

The worst case is a condition called dead pool – when water levels drop lower than the lowest release valves, like the dregs beneath the spigot of a jug.

As it is, the National Park Service announced this week that toxic blue-green algae had been detected in Blue Mesa, a phenomenon that happens in shallow, warm water.

“Those poor hydrologic conditions … really put us in these dire circumstances,” Foy said.

To preserve habitat for endangered fish species protected by law, the Bureau of Reclamation typically tries to keep at least 1,050 cubic feet per second of water flowing past a meter at the base of the Gunnison near where it joins the Colorado River. Foy said, in the course of this year, that target has dropped from 900, to 750 and finally to 500 cubic feet per second.

Limiting downstream releases has allowed more water to stay in reservoir storage. Hopefully, it’s enough to last through to next spring’s runoff. Hopefully, unlike this year, there will be an appreciable spring runoff.

Foy said the Blue Mesa was in uncharted territory.

“It’s really never been drawn down to this level at this time of year,” he said.

It’s far from alone. Many of the rivers and reservoirs fed by Rocky Mountain snowmelt are at extreme lows this year. Water restrictions are widespread. Many of Colorado’s agricultural regions have cut back on crops or livestock herds. Colorado Parks and Wildlife has six current emergency fish salvages in place, according to the Colorado Fishing Atlas.

Bart Miller, Healthy Rivers director at environmental advocacy organization Western Resource Advocates, thinks this year might be a wake-up call for water policymakers.

“There will be more years like this in the future,” he said.

Negotiations on how to manage the Colorado River Basin have been gridlocked for years. Two weeks ago, the Bureau of Reclamation released its plan for management instead of an agreement among the states, which calls for major water use reductions for Arizona, California and Nevada. The old operating guidelines from 2007 are set to expire Oct. 1.

Miller anticipates irrigators in Colorado will have more federal incentives to cut back on water use in the future. By necessity, they already have. Pope said the Uncompahgre Valley Water Users Association has had restrictions in place in 20 of the last 25 years.

“We just have to live with whatever Mother Nature provides us,” he said.