The Henry’s Fork Foundation was notified in mid-June about plans to release water from the Island Park Reservoir to provide extra flows for a turbine test at Chester Dam June 21-26. Through negotiations with Fall River Rural Electric and other entities, it was decided to delay the release and the testing until later in July to provide more notice for travelling anglers and to maintain the great June angling opportunities on the Henry’s Fork.
Starting Tuesday, July 21, flow will increase by 900 cfs at Island Park Dam, resulting in a flow of 2,000 cfs for about two to three days. However, due to continued plant growth in the channel since the stream gage was last adjusted on July 10, this actual flow of 2,000 cfs will appear as 2,200 cfs on the USGS real-time flow data web site.
Flows of this magnitude are not unprecedented. Maximum flows on record out of Island Park Dam for mid- to late-July are between 2,300 and 2,600 cfs. Flows equaling or exceeding 2,000 cfs occur in roughly 4% of all water years. Highest July flows on record occurred in 1955, 1959, and 1984. During these years, flows exceeded 2,000 cfs for extended periods. For example, in 1984, outflow from Island Park Dam exceeded 2,000 cfs from July 11 to August 20, a total of 41 days.
Please be cautious when wading due to swifter flows and slightly deeper water. The health of the fish population will not be affected, and higher flows will probably be beneficial to the fish populations in certain stretches of the river. Flows from Island Park Reservoir will be adjusted to near 1,000 cfs after the test is complete, no later than Friday, July 24.