ALBUQUERQUE, N.M. (AP) — Federal water managers will be facing difficult decisions as the worsening drought is significantly affecting flows on one of the country's longest river systems and prompting rescue missions for a tiny endangered fish.

The U.S. Bureau of Reclamation and U.S. Army Corps of Engineers released their operating plan for the Rio Grande on Thursday.

With some of the lowest snowpack reports on record, officials said they will have very little water this season as they decide when and how best to move what is stored in the reservoirs for downstream users and for the Rio Grande silvery minnow.

The tiny fish, listed as endangered in 1994, was once abundant throughout the Rio Grande Basin from Colorado to Texas and into Mexico. It's now found only in a fraction of its historic habitat as the river system has seen dam building and the straightening of its once meandering channels over the last 150 years.

The minnow population just five years ago marked one of the lowest levels since surveys began in the mid-1990s. At that point, the fish was showing few signs of reproduction in the wild and that year's fast moving drought left biologists trying to salvage as many of the minnows from puddles in the drying river.

This year, water managers say more than 10 miles of the river have already dried in the area of Bosque del Apache National Wildlife Refuge.

They warned during a briefing Thursday that residents in the Albuquerque area — the state's most populous region — should be prepared to see a dry riverbed later this spring and summer.

The Bureau of Reclamation said in a statement it is coordinating with the U.S. Fish and Wildlife Service to ensure fish rescue crews are active in areas of the river that have dried.

The Bureau of Reclamation also is working with other agencies to coordinate river operations to ensure there's a bump in spring flows for spawning and egg collection.

The bureau has about 11,600 acre-feet of water available to supplement flows through the Middle Rio Grande and is currently releasing about 200 acre-feet. One acre-foot (1,233 cubic meters) is enough to supply a typical U.S. family for a year.

In southern New Mexico, little runoff is expected reach to Elephant Butte Reservoir this spring. Federal officials say it could be left holding less than 5 percent of its capacity by the end of the irrigation season.