Colorado’s Cache la Poudre River tumbles 80 miles from its high-alpine headwaters in Rocky Mountain National Park down to the South Platte River on the plains below. The upper Poudre is the only designated wild and scenic river in the state – but after it exits Poudre Canyon, 90 percent of its flow is siphoned off for farmers and homeowners around Fort Collins. Now, a local water district wants to tap the remaining 10 percent to fill two new reservoirs.

Municipal planners in northern Colorado say the prospect of drought combined with a booming population (predicted to increase three-fold by 2050), leaves only one solution: more water storage, in the form of the Northern Integrated Supply Project. “This is not a case of ‘if you don’t build it, they won’t come,’ ” says Carl Brouwer, project manager. “Bottom line: More people equals the need for more water.”

The Army Corps of Engineers project includes not only the two reservoirs, but also pump stations and pipelines. Water from the South Platte River will fill the 40,000 acre-foot Galeton Reservoir, on the plains five miles northeast of Greeley. The much-larger Glade Reservoir – with a capacity of 170,000 acre-feet – will use Poudre River water to inundate a mountain valley about 10 miles north of Fort Collins.

Two-thirds of Glade’s water would come from existing diversions for agriculture, while the remainder would be pulled from the Poudre in peak-flow years, which occur about once every four years. That would cause a significant decline in peak-flow volumes – and therein lies the problem.

“The peak flow is absolutely critical to the ecological health of the river,” says Gary Wockner, ecologist and member of Save the Poudre, a citizen’s group opposing the project. Peak flows recharge the wetlands that filter out pollutants such as ammonia, and redistribute silt, which creates spawning beds for trout and seedbeds for new cottonwoods. “If there is no peak flow, critical habitat and sand bars disappear and seed dispersal no longer occurs,” says Wockner. “Lose the peak flows and lose the wetlands.” Municipal planners, however, say mitigation efforts, such as minimum stream flow levels and the construction of “low flow channels” for fish during drought periods, will protect the Poudre’s fragile ecosystem.

The Northern Colorado Water Conservation District says that the new reservoirs are crucial for preserving Colorado’s agricultural roots. The project would provide an annual 40,000 acre-feet of water to 15 communities and water districts in Weld, Larimer, Boulder and Morgan counties. Those counties face the loss of much of their farmland as cities buy agricultural water rights. By providing municipal users with an alternative water supply, the project will prevent the permanent dry-up of 25,000 acres of farmland, according to the water district.

But because the $400 million project is debt-funded, it relies on population growth and the subsequent newcomers to pick up most of the costs. “What the general public doesn’t realize is that (the Northern Integrated Supply Project) actually promotes a vehicle to pave over farms,” says Wockner. “The exact growth that NISP relies on financially will occur on 20,000 acres of irrigated farmland in northern Colorado.”

Wockner and other conservationists say that northern Colorado can meet its future water needs without further draining the lower Poudre. They recommend conservation and education, coupled with modest improvements in agricultural irrigation efficiency. “Northern Colorado has lots of small towns with big dreams of growing as quickly as possible,” says Mark Easter, conservation chair for the Sierra Club’s Poudre Canyon Group. “And most of them don’t have any water conservation or efficiency plans in place.”

Municipal planners agree that water conservation efforts are important, but say that conservation alone cannot solve the region’s long-term water shortage. The Army Corps of Engineers is expected to release its draft environmental impact statement near the start of the New Year, and members of Save the Poudre are already calling for a doubling of the traditional 90-day comment period.

“This is a huge decision – ground zero for the next phase of dam building in the West,” says Wockner. “This truly is a watershed issue.”