In deciding the amount of water it will release, the agency factors in Upper Klamath Lake’s level, a water supply forecast, how much water irrigators will use — which varies depending on how dry the summer will be — and biological opinions.

   Biological opinions from the U.S. Fish and Wildlife Service and National Marine Fisheries Service mandate certain water elevations for Upper Klamath Lake and flow rates for Klamath River in order to protect endangered fish — sucker and coho salmon.

   The crux of the equation is inflows.

   The National Resource Conservation Service starts tracking snowpack in October, the beginning of the new water year, and issues its first water supply forecast in January.

   Each month until April the agency looks at snowpack and snowmelt to predict how many acre-feet of water — a volume of one acre of surface area, one foot deep — will be available for groups that depend on lake water.  

   Water supply forecast

   The Bureau of Reclamation’s water operation plan is based on the water supply forecast, said Jon Lea, National Resource Conservation Service snow survey supervisor for Oregon.

   Inflow predictions in the April water supply report are the base for the entire watering year, Lea said, but as the season progresses, the agency can adjust the amount of water it releases.

   This year, for example, on-Project irrigators were allowed 150,000 acre-feet from Upper Klamath Lake for the season, but received another 35,000 acre-feet in July as conditions improved.