Colorado's water crisis reached a stark new milestone this week when federal officials reported that Blue Mesa Reservoir, located near Gunnison, had dropped to a level not seen in the modern era. By falling to less than 25% of its capacity, Blue Mesa has lost its status as the state's largest body of water — a title now held by Lake Granby, itself only 62% full.

The ruins of Iola, a community flooded during the creation of Blue Mesa, are now visible, and parts of the Gunnison River snake through the lakebed in imitation of its historic path before the reservoir was dammed in the 1960s. A volunteer at the Gunnison Pioneer Museum who drove past the reservoir this week described the scene plainly. "You could absolutely see the river, and you could kind of imagine what it was like before," she said.

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. A senior water resources engineer at the Colorado River Water Conservation District said Blue Mesa was in uncharted territory, noting that "it's really never been drawn down to this level at this time of year."

The reservoir's decline carries consequences well beyond the lakebed. The Uncompahgre Valley Water Users Association relies on water stored in Blue Mesa, which is diverted downstream through the Gunnison Tunnel to irrigate tens of thousands of acres of farmland, while 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 the manager of the association said that source is "nonexistent" this year, and in anticipation of shortages the association already limited users to 50% of their allocations this spring. Large row crop producers have already fallowed 30% to 60% of their land in the valley.

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 — the threshold below which its 86.4-megawatt generators, capable of powering roughly 3,400 homes, can no longer produce hydroelectric power. The National Park Service also announced this week that toxic blue-green algae had been detected in Blue Mesa, a phenomenon that occurs in shallow, warm water.

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, and Colorado Parks and Wildlife has six current emergency fish salvages in place. Negotiations on how to manage the Colorado River Basin have been gridlocked for years, and two weeks ago the Bureau of Reclamation released its own management plan — rather than an agreement among states — calling for major water use reductions for Arizona, California, and Nevada, as the existing 2007 operating guidelines are set to expire October 1.

Whether Blue Mesa can hold sufficient water through the winter to avoid further emergency restrictions before next spring's runoff remains the central question water managers are watching.