ALBUQUERQUE, N.M. (AP) – Environmentalists are crying foul over a water exchange between the federal government and the city of Santa Fe, saying the deal could compromise flows along the middle Rio Grande next spring.

The group WildEarth Guardians sent a letter to the U.S. Interior Department on Friday, saying such transactions should be transparent and that policies need to be changed to allow for the river’s flows to be better protected.

The dispute stems from an agreement reached this fall between the Bureau of Reclamation and Santa Fe. They traded water stored in Elephant Butte Reservoir in southern New Mexico for water stored for six Native American communities in El Vado Reservoir in the north.

The exchange on paper meant no water would physically flow down the river and the amount secured by the bureau isn’t enough to provide for a peak flow in the spring, the group said in its letter.

“It is not likely that Reclamation will have enough water to generate even a modest peak flow in the spring of 2015,” the group wrote. “This upcoming spring will be the sixth year without a peak flow in the middle valley, pushing endangered species further toward the brink of extinction.”

The bureau said Tuesday it’s continually seeking management options for meeting the needs of all water users and species but operations are bound by federal and state law, including reservoir authorizations and interstate water compacts.

“Reclamation is highly dependent upon the cooperation of multiple partners in the middle Rio Grande and cannot provide flows for environmental purposes without substantial coordination,” the agency said in a statement.

Mountain ranges across northern New Mexico and southern Colorado – the headwaters of the Rio Grande – have received little meaningful snow in recent years. That dismal snowpack combined with warmer temperatures have resulted in less spring runoff and less water finding its way to the Rio Grande.

Environmentalists have been fighting to keep the river flowing to benefit the endangered silvery minnow and other species.

In 2013, the bureau brokered a deal with the Albuquerque-Bernalillo County Water Utility Authority to exchange and carry over water that was stored in El Vado. Rather than releasing the water in December like usual, officials saved it and released it in the spring to help mimic the river’s peak flows. Officials were unable to reach a similar agreement this year.

Jen Pelz of WildEarth Guardians said creating a new policy that would provide for storage of the water with a portion going specifically to environmental purposes could result in a “water safety net” for the Rio Grande Basin.