Timely rain storms throughout the upper Snake River region during September have improved the outlook for river flows and overall water supply in the Henry's Fork watershed. This is good news for wild trout in the Henry's Fork.
Despite predictions early in the summer that Island Park Reservoir could be drawn down to 10,000 acre-feet (7.4 percent of capacity), the reservoir reached a minimum of just over 35,000 acre-feet (26 percent of capacity) in late September.
Rains and cool weather ended withdrawal of storage water for irrigation a few weeks earlier than usual, allowing water managers to leave more storage in Island Park Reservoir to carry over into the winter storage season.
This additional water will allow December-February flows in the Henry's Fork to be around 150 cubic feet per second (cfs), versus the 110 cfs that had been projected earlier in the summer.
September rains pushed water-year total precipitation up to 87 percent of average in the Henry's Fork watershed and 91 percent of average in the larger upper Snake River basin. Near-average precipitation is forecast for the region during the October-December period.
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