LIHI Certificate #2 – Island Park Project, Idaho

Island Park Dam, Reservoir, and Hydroelectric Project is located in eastern Idaho within the Island Park District of the Targhee National Forest; the reservoir covers 7,794 acres within the Forest. The headwaters of the Henry’s Fork River begin 31 miles above the dam, at Henry’s Lake.

The Island Park Dam was constructed in 1939 by the USBR. The Island Park Hydroelectric Project was licensed in 1988 and constructed between September 1992 and July 1994 on the existing USBR Island Park Dam. The Hydroelectric Project consists of the screened intake structure with 3/8 inch openings, approximately 720 feet of a 10-foot diameter penstock, a concrete masonry powerhouse with two vertical Francis turbines/generators and associated controls, one 500 hp. centrifugal blower, one 250 hp. positive displacement blower, one 200 hp. variable speed blower with associated controls, a 60’ x 100’ aeration basin, and a concrete masonry valvehouse located on top of the dam. The aeration basin, powerhouse, and a small section of the buried penstock are located at the base of the Island Park Dam. The land occupied by project facilities is under the jurisdiction of the U.S. Forest Service (USFS); the hydroelectric project operates under a special use permit issued to the licensee by the USFS, dated April 23, 1992. The total acreage of USFS lands affected by project features is 1.2 acres. The Island Park Hydroelectric Project utilizes waters diverted from the Island Park Reservoir under the direction of the Fremont-Madison Irrigation District and the USBR.

Reservoir Operations

Island Park Dam is a 9,448-foot long earthfill structure with a maximum height of 91 feet. The Dam provides 127,265 acre-feet of storage for irrigation demands by the Fremont-Madison Irrigation District. The other considerations in the operation of the reservoir are water rights, the system operating goal of holding water in upstream space, and opportunity to exchange stored water with other reservoirs to accomplish multipurpose objectives. The reservoir is full at an elevation of 6,303 feet, with a surface area of approximately 8,084 acres. The reservoir is filled no later than April 1 of each year; releases for irrigation occur during the spring and summer months (particularly July and August). The Island Park Dam releases water downstream through an outlet tunnel (3,400 cfs capacity) at the base of the dam. Water reaches this tunnel by two means: through a low level (6,239 elevation, reservoir bottom) intake in the reservoir, and through a “bathtub” spillway at elevation 6,302 adjacent to the dam (There is no “spill” over the top of the dam or other releases from the face of the dam). Under normal operating conditions, the uncontrolled “bathtub” spillway is utilized when the reservoir exceeds an elevation of 6,302 feet (spillway crest elevation). The water elevation over the spillway height of 6,302 feet determines the amount of outlet flow downstream. Starting in the fall, releases through the outlet tunnel are reduced to ensure that the reservoir surcharges to at least 6,303 feet by April 1. The outlet tunnel may be closed completely with all water leaving the reservoir from the surface spillway. Total USBR outlet flows are comprised of the sum of the uncontrolled spill and the low-level outlet gate openings.

Hydroelectric Project Operation

The Island Park Hydroelectric Project operates with water diverted though a screened intake near the bottom of the reservoir. The water is piped through the Island Park Dam into the Island Park powerhouse constructed at the base of the dam. After leaving the powerhouse, water is released through a tailrace into an “aerating basin” where blowers are used to aerate the tailrace releases (low in dissolved oxygen since they originated from near the bottom of the reservoir). Because the USBR has complete control over releases from the dam, the Project does not release a required minimum flow. The Project does target ramping rate flow releases of 30 cfs - 35 cfs per half hour and releases no greater than 50 cfs per half hour.

Project Name Island Park
LIHI Certificate No. 2
LIHI Certificate Term December 30, 2016 - December 29, 2021
Owner Fall River Rural Electric Cooperative, Inc.
State Idaho
Location Located at river mile 91 on Henry's Fork of the Snake River 0.4 miles upstream of its confluence with the Buffalo River, and approximately 40 miles north of Ashton in Fremont County, Idaho.
Installed Capacity 4.8 MW
Average Annual Generation 19,437 MWh
Facility Type Diversion
FERC No. P-2973 issued 1988, expires 2038

Certification History

January 29, 2018: The appeal period for the Preliminary Decision to Certify the Island Park hydroelectric project has closed with no requests to appeal. The decision is therefore final. Island Park is LIHI Certificate #2.

December 27, 2017: The Island Park Hydroelectric Project, ID (LIHI #2) on Henry's Fork of the Snake River in Idaho, has been granted preliminary Low Impact Certification.

The Island Park Hydroelectric Project Certification includes the following condition:

  • Condition 1: In its annual compliance report, the Owner shall report on any FERC Order or FERC  correspondence in response to the Owner Agent’s notice to FERC dated December 13, 2017  regarding the status of license article 401 and dissolved oxygen measurements. The Owner  shall provide a status update on progress in rectifying differences between state water  quality standards and FERC license requirements with the annual compliance statement  submitted to LIHI. LIHI reserves the right to review or cancel certification and/or modify or  add conditions based on the outcome of these matters.

As provided for in the LIHI Certification Handbook, the preliminary decision will be followed by a 30-day period to appeal the decision. Appeal requests may be submitted by those who provided comments during the application's 60-day public comment period. Any appeal must include specific reasons why the appellant believes the hydropower facility does not meet one or more criteria. Appeal requests can be submitted by email to with "Island Park Hydroelectric Project" in the subject line, or by mail addressed to The Low Impact Hydropower Institute, 329 Massachusetts Ave, Suite 2, Lexington, MA 02420.  All requests will be posted to this website and the applicant will have an opportunity to respond. Any response will also be posted. Requests must be received by 5pm EST on January 26. More details on the appeal process can be found in our handbook HERE.

December 30, 2016 – On December 23 3016, the Low Impact Hydropower Institute (LIHI) received a complete application from Fall River Rural Electric Cooperative, Inc., for the Low Impact Certification of the Island Park Hydroelectric Project (FERC No. 2973), located on Henry's Fork of the Snake River at approximately river mile (RM) 91, 0.4 miles upstream of its confluence with the Buffalo River, and approximately 40 miles north of Ashton in Fremont County, Idaho.

The Island Park project was first certified as low impact  by LIHI as Certificate No. 2 on June 7, 2001 for a two year term, ending on June 7, 2003.  The certification was extended in 2003 when LIHI extended certification terms from two years to five years in duration.  It was certified again for a five year term from June 24, 2006 to June 24, 2011.

LIHI is seeking public comment on this application. Specifically, we are interested in knowing whether you think the Island Park project meets the LIHI Low Impact Certification Criteria. The Island Park application is subject to review using the Criteria in the LIHI Certification Handbook of 2014.  Please review the program and criteria in LIHI’s 2014 Handbook and then review the Project’s 2016 application materials posted on the project page. Comments that are directly tied to specific LIHI criteria (flows, water quality, fish passage, etc.) will be most helpful, but all comments will be considered. Comments may be submitted to the Institute by e-mail at with “Island Park Project Comments” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, PO Box 194, Harrington Park, New Jersey 07640. The 60 day public comment period begins on January 3, 2017.  Comments must be received at the Institute on or before 5 pm Eastern time on March 4, 2017 to be considered. All comments will be posted to the web site and the applicant will have an opportunity to respond.  Any response will also be posted.

The Island Park comment period has been extended to March 6, 2017.