After rapid snowmelt in May, streamflow in the upper Henry’s Fork subwatershed (Island Park) dropped back to alarmingly low levels. Natural watershed inflow between Henry’s Lake and Island Park is well below average, indicating low inputs from springs; after outflow from those springs had only just started to approach average following the 2013-2016 drought. Peak snow water equivalent (SWE) has been below average in 12 of the past 21 years at the two sites we track on the Yellowstone Plateau, the source of recharge for those springs.
Over the Ranch opener, Island Park Dam outflow will simply be the river’s natural flow (likely 600-650 cfs) as the reservoir is kept full until draft is needed to meet irrigation need at the end of June. Thank you to the US Bureau of Reclamation for filling Island Park Reservoir effectively this spring and we will continue to work with partners to make the most of the water Mother Nature has given us. Many of HFF's key programs are designed to do just that; to ensure favorable streamflow, good water quality, and a positive fishing experience in the face of changing water availability.