LIHI Certificate #67 - Stillwater Hydroelectric Project, Maine

Note: The original Stillwater Project, referred to as Powerhouse A was certified by LIHI as Project #67 from June 1, 2010 to June 1, 2015.  A second certification application was submitted for a newly constructed Powerhouse by Black Bear Hydro Partners (BBHP), which also received LIHI certification from August 7, 2013 to August 7, 2018 as LIHI Project # 110. It was agreed that combining both projects into one would make sense for recertification consideration, and the two are referred to as the Stillwater Project, LIHI #67.

The Stillwater Project is located on the Stillwater Branch of the Penobscot River ("River) in Old Town, Penobscot County, Maine. The Penobscot River Basin ("Basin") is New England's second largest river system with a drainage area of 8,570 square miles. Upstream storage dams on both the West and East Branches control a large portion of flows within the drainage area. The Basin includes the East and West Branches of the Penobscot River, the Piscataquis River, the Sebec River, the Pleasant River, the Mattawamkeag River, the Passadumkeag River, the Stillwater Branch and the main stem of the Penobscot River, as illustrated on the following page. The Stillwater Project is located on Stillwater Branch of the Penobscot River, approximately three miles downstream of the Gilman Falls Dam (which is part of the Milford Hydro Project) and about one mile upstream of the Orono Dam. The Mattawamkeag River remains free-flowing, while there are a total of 20 run-of river dams located on the other Basin waterways.

The existing Stillwater Project works consist of a main concrete gravity dam, totaling about 1,720 feet long, with a maximum height of 22 feet at crest elevation 91.65 feet; a concrete and wooden powerhouse; four horizontal hydroelectric generating units, all totaling a rated capacity of 1,950 kilowatts (kW); an impoundment about 3.1 miles long, having a surface area of about 300 acre, a gross storage capacity of 3,040 acre-feet, a negligible useable storage capacity, a normal headwater surface elevation of about 94.65 feet; a downstream fishway bypass; and appurtenant facilities. The re-development of the Project included a second powerhouse containing three turbine-generating units having a nameplate capacity of 803 kW per unit. The powerhouse is located adjacent to the existing left buttress of the dam. A new 60-feet-wide forebay intake will supply the powerhouse. The new powerhouse intake includes a 60-feet-wide by 22-feet-high trashracks with angled 1-in clear spacing. The tailrace will discharge to the existing pool in the bypass reach. The new powerhouse began generation in September 2013.

As part of the redevelopment, BBHP installed a new downstream fishway at the new powerhouse, refurbished the existing downstream fishway located near Powerhouse A, constructed an upstream eel passage facility at the top of the forebay, developed downstream passage for eels and added one-inch trashracks for the full depth of the new and existing powerhouse intakes. More detail on these fish passages, including some photographs, can be found in the original certification reports.

The Stillwater Project is operated as a run-of-river development with discharge from the project turbines and spillway equivalent to inflow.  Flows are reallocated between the main stem of the Penobscot River and the Stillwater Branch through operation of its Milford Project (No. 2534).  The Stillwater Project includes a downstream bypass that discharges to the tailrace. The Stillwater Project also includes two upstream fishways for juvenile American eel that are located at the east and west abutments of the spillway. The Project provides a minimum flow to the bypass reach of 195 cfs through weirs located near the west abutment (70 cfs) and near the center of the spillway (125 cfs).

The Stillwater Project commenced initial commercial operations in 1913.  The Stillwater Project generates clean, renewable electricity while providing recreational opportunities (portage trail, parking areas for river access and hand-carried boat launch), fish passage measures, consistent water levels that enhance habitats for waterfowl, etc., and substantial support of the local community through stable property tax payments, reliable voltage support of the electrical distribution system, etc.

The Stillwater hydroelectric project is a component of the Penobscot River Restoration Agreement. The overall intent of the Agreement is to provide enhancements to the Penobscot River's environmental resources, and lower and minimize the influence of BBHP's hydroelectric projects on those resources while maintaining the levels of renewable hydropower generation from the river. This restoration effort is one of the largest river restoration projects in our nation's history. In an unprecedented collaboration, a diverse group of stakeholders are working together to restore 11 species of sea-run fish to the Penobscot River, while maintaining energy production.

On June 25, 2004, the Lower Penobscot River Basin Comprehensive Settlement Accord (“Lower Penobscot Agreement”) was signed. The Agreement represented an unprecedented collaboration to restore 11 species of sea-run fish while rebalancing hydropower generated on the river.  An integral part of the energy balance associated with the Agreement included amending the license for the Stillwater Hydroelectric Project.  In June 2004 an application was filed with the Federal Energy Regulatory Commission (“FERC”) for the amendment and FERC issued the amendment on April 18, 2005 (111 FERC 62,065).

Parties to the Lower Penobscot Agreement include Black Bear Hydro Partners, LLC’s predecessor PPL Maine, LLC; the  Penobscot Indian Nation (Penobscot); U.S. Department of the Interior (Interior); Maine State Planning Office, Maine Atlantic Salmon Commission, Maine Department of Inland Fisheries and Wildlife, and Maine Department of Marine Resources (“Maine Agencies”); American Rivers, Inc., Atlantic Salmon Federation, Maine Audubon Society, Natural Resources Council of Maine, and Trout Unlimited; and the Penobscot River Restoration Trust (“Trust”).

Project Name Stillwater & Stillwater B
LIHI Certificate No. 67
LIHI Certificate Term June 1, 2015 - June 1, 2020, extended to March 15, 2021
Owner Black Bear Hydro Partners, LLC
State Maine
Location Located at river mile 2.4 on the Stillwater Branch of the Penobscot River in Old Town, Maine.
Installed Capacity Total: 4.18 MW Powerhouse A: 1.951 MW Powerhouse B: 2.229 MW
Average Annual Generation Total: 32,521 MWh Powerhouse A: 14,221 MWh Powerhouse B: 18,300 MWh
Facility Type Run-of-river
FERC No. P-2712 issued 1998, expires 2048

Certification History

December 1, 2020: The Low Impact Hydropower Institute has received a complete application for Low Impact recertification of the Stillwater Project. The complete application can be found below.

LIHI is seeking public comment on this application. 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 “Stillwater Project Comments” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, 1167 Massachusetts Avenue, Arlington MA 02476. Comments must be received on or before 5 pm Eastern time on January 30, 2021 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.

February 12, 2017:  The 30-day appeal period ended with no appeals received. Therefore, the Stillwater Project LIHI Certification is final and the effective certification date for the Stillwater Project is June 1, 2015 for a five (5) year term, which will expire on June 1, 2020.

January 18, 2017: On January 13, 2017, LIHI Executive Director Shannon Ames, using authority delegated from the LIHI Governing Board, has issued a Preliminary Certification Decision that the Stillwater Hydroelectric Project (FERC No. P-2712) satisfies the LIHI Certification Criteria.  This certification decision is based on authority delegated from the LIHI Governing Board.  The certification includes four facility-specific conditions, as follows:

Condition satisfied 2018. Condition 1.  The Owner shall notify LIHI within 30 days of receipt of USFWS certification of the downstream anadromous fishway and of the up and downstream eel passage facilities as required by the Lower Penobscot River Multiparty Settlement Agreement. This certification requires affirmation that a) the facilities were designed and installed as prescribed, b) the facilities are ready for routine operation as evidenced by approved Operating Manuals and electronic data collection systems and c) one year of testing and any required “fine tuning” has been completed. If such USFWS certification is not received by the end of 2017, the Owner shall provide LIHI documentation as to why the certification has not been received and the plan and schedule to remedy deficiencies identified by USFWS preventing such certification.

Condition 2.  If the requirement for re-initiation of studies of downstream passage of juvenile alosine species occurs within this LIHI certification period, the Owner shall notify LIHI within 60 days of receipt of such study re-initiation. This notification shall include the study schedule including the expected report issuance date. A copy of the final report, along with agency comment as to whether or not the testing results prove that safe downstream passage has been demonstrated, shall be provided to LIHI within 60 days of issuance of the final report.

Condition 3.  The Owner shall notify LIHI within 60 days of receipt of USFWS, NMFS and MDMR acknowledgement that the standards specified in the Biological Opinion for safe downstream passage of Atlantic salmon have been met. Currently, effectiveness testing should be completed by 2018 based on the three-year testing requirement, unless advancement to the third level flow enhancement sequence is found to be necessary. Should this occur, the Owner shall notify LIHI in the annual compliance report as to the new date by which such continuing testing to meet passage standards is expected to be completed.

Condition 4.  The Owner shall provide LIHI a summary of the results of the 2016 quantitative downstream effectiveness study for American eel, along with comments received from USFWS, NMFS and MDMR as to whether or not the testing results prove that safe downstream passage for American eel has been demonstrated. Also, the Owner shall provide a summary of the annual American eel upstream passage results, along with confirmation that any changes to the passage facilities recommended by the resource agencies have been implemented or are scheduled for implementation. The noted upstream and downstream passage results shall be provided within 60 days of report finalization.

As provided for in Section 4.2.5 of the LIHI 2nd Edition Handbook, the Preliminary Certification Decision, along with the Application Reviewer’s report and (if prepared) report of the Executive Director, will be posted on the Institute’s Web page for 30 days.  Notice of the posting will be provided to all individuals or organizations that commented on the initial Application Package.

Any Commenter may submit a letter to the Executive Director requesting an appeal within the 30-day period, which begins on January 20, 2017 and ends on February 20, 2017.  The appeal request must state specific reasons why the hydropower facility should have failed one or more criteria.  Only individuals or organizations that commented on the initial Application Package may file an appeal.  Further information about the LIHI appeal process is available in the LIHI Handbook, available at

If no appeal is requested within the 30-day period, the Executive Director will issue LIHI Certification for the facility and post a notification of certification on the Institute’s website.  Once final, the effective certification date for the Stillwater Project is June 1, 2015 for a five (5) year term, which will expire on June 1, 2020.

December 11, 2015: The Low Impact Hydropower Institute has received a complete application for a new term of Low Impact Certification for the Stillwater Hydroelectric project.  The application materials can be found in the Files section below.

The public comment period for this application closed on February 12, 2016.

January 28, 2011: The Stillwater Hydroelectric Project has been certified as low impact for a five year term, effective June 1, 2010 and expiring June 1, 2015.

August 2, 2010: The public comment period for the application for certification has been closed.

June 2, 2010: Black Bear Hydro Partners has submitted an application for the certification of the Stillwater Project. Public comment period will be open for 60 days.

2020 Recertification