• Between First and Second Levels:
• Boatlock: The powerhouse structure is an L-shaped building with a concrete substructure and a brick superstructure. It dates from the early1920s and houses one 700-kW unit, one 1,200-kW unit, and one 1,440-kW unit. All are vertical axis Francis units. The 1,200-kW unit underwent a complete generator overhaul and rehabilitation from June 2014 to May 2015.
• Beebe-Holbrook: The powerhouse is a concrete and brick structure. It dates from the late 1940s and houses one 266-kW vertical-axis Francis generating unit.
• Skinner: The station is located 1,600 feet south of the Beebe-Holbrook Station and is housed in a non-project building. The installation dates from 1924. Water is delivered through a 150-foot-long, 9-foot diameter steel penstock. There is one 300-kW vertical axis Francis unit.
• Holyoke 1: The powerhouse is a brick structure constructed in 1893. It contains two 230-kW and two 270-kW turbine generators. Other facility works include two steel penstocks 10 feet in diameter and 36.5 feet long and two tailraces 328.5 feet long and 20 feet wide.
• Holyoke 2: This facility commenced operation in 1938. Project works include an intake at the wall of the Holyoke first level canal; two parallel 9-foot diameter steel penstocks each 240 feet long; one surge tank about 17 feet high and 10 feet in diameter; a powerhouse containing one vertical turbine-generator unit rated at 800 kW; and two parallel brick arched tailrace conduits, each 9 feet wide, 10 feet high and 120 feet long, discharging into the Holyoke second level canal.
• Holyoke 4: This facility includes two 7-foot-diameter, 76-foot-long penstocks which draw water from the first level canal to the powerhouse equipped with two 375-kW generating units. Two 13-foot-wide, 300-foot-long tailraces discharge into the second level canal.
• Between Second Level and the Connecticut River:
• Riverside: The station has two distinct powerhouses made of concrete and brick. Units 4-7 are housed in one structure. Unit 4 is an 880-kW turbine-generator and Unit 5 is a 600-kW turbine generator; both are horizontal Francis turbines. Unit 6 is also a horizontal Francis unit rated at 600 kW but has been partially dismantled and placed in deactivated reserve status. Unit 7 is a 1,560-kW vertical-axis Francis turbine-generator. Unit 8 is housed in a separate powerhouse and is a vertical axis propeller turbine-generator rated at 4 MW.
• Valley Hydro (Holyoke 5): Project works consist of a gated intake with trashracks; two 75-foot-long, 6.5-foot-diameter steel penstocks; a refurbished vertical Kaplan turbine-generator rated at 790-kW; a 375 foot long, 16.5 foot wide, and an11-foot-high arched brick-lined tailrace tunnel.
• Between Second and Third Levels:
• Holyoke 3: The station commenced operation in 1940 and includes an intake trashrack about 47 feet long and 11 feet high; two head gates about 11 feet square; two low pressure brick penstocks, each roughly 85 feet long and 93 square feet in cross section; a reinforced concrete powerhouse which houses one turbine generator unit rated at 450 kW; and an open tailrace about 118 feet long, 30 feet wide, and 10 feet deep.
• Between Third Level and Connecticut River:
• Chemical: The facility is located in a non-project industrial building with water delivered through a masonry flume about 260 feet long and 22 feet wide. The facility’s building is constructed of concrete and brick. There are two generating units, one a vertical-axis Kaplan set rated at 800 kW and the other a vertical-axis fixed blade set, also rated at 800 kW. The units were installed in 1935. The tailwater is carried to the river by two covered masonry flumes, each 125 feet long, 15 feet wide, and 9.5 feet high.

The project operates in run-of-river mode. Inflows to Holyoke Dam are highly regulated by upstream operations at Turner Falls and Vernon. Impoundment fluctuations are limited to 1.2 feet for protection of the endangered Puritan tiger beetle. Minimum flows of 840 cfs are provided into the three channels of the bypass reach and adjusted up to 1,300 cfs for the fish passage season. A total discharge of 550 cfs is also released into the canal system – 150 cfs for the operation of the downstream fish passage facility and 400 cfs for protection of aquatic biota, specifically mussels. The flow regimes were developed in consultation with Massachusetts Department of Environmental Protection (MADEP) and Massachusetts Division of Fish and Wildlife (MADFW).

Waters within the project reach are listed as impaired for E. coli, PCBs in fish tissue, and total suspended solids. Consultation with MADEP concluded that none of the listed impairments are contributed to by the project. The project monitors water quality at the project developments and reports annually to MADEP with the results.

Upstream fish passage is provided for migratory fish and American eel. The passage facility consists of two fish lifts which have been successful in passing shortnose sturgeon (a federally endangered species) and other anadromous species (American shad, Atlantis salmon, sea lamprey, and river herring) and four ramp traps provide passage of American eel. A downstream fish passage louver facility is located in the canal about 550 feet downstream of the canal gatehouse to prevent fish from entering the canal system. An eel ramp, bypass pipe, bypass weir and spillage provide adequate downstream passage for migratory species.

The project lands are completely located within a heavily developed, urban environment. No lands of significant ecological value are found in the project area. The project developed a Shoreline Erosion Remediation Plan which included provisions for inventorying, evaluating, monitoring, and remediating shoreline erosion problems at the project.

Threatened or endangered species potentially present in the project vicinity include the Puritan tiger beetle, bald eagle, yellow lampmussel, Atlantic sturgeon, and shortnose sturgeon. One of the primary reasons the project modified operations from peaking to run-of-river was to protect the Puritan tiger beetle populations that were found along the project boundaries. This operational modification also helped enhance downstream habitat for aquatic species. The National Marine Fisheries Service was consulted to determine the impact of the project on sturgeon populations. There is potential for critical habitat to occur downstream of the project but outside of the project boundary. Thus, operations have generally benefitted the downstream flow regime, enhancing the habitat and minimizing any adverse impacts.

The Holyoke and South Hadley canal systems are both listed as Historic Districts on the National Register of Historic Places. Unfortunately, upgrading of the fish passage facilities in 2015 resulted in adverse impacts to a submerged timber crib dam and a 1950s-era cofferdam, both contributing elements to the Holyoke Hydropower System Historic District. The project owner collaborated with the State Historic Preservation Office (SHPO) to preserve photographs of the resources and salvage some pieces of wood from the timber crib dam as part of it had to be removed in the passage facility upgrade. This was done in coordination with the Holyoke Historical Commission. Additionally, the historic Texon Mill was demolished after several failed attempts at adaptive reuse of the building. An agreement was made between the Army Corps of Engineers, the SHPO, and the South Hadley Selectboard and Historic Commission to demolish the mill, clean up the site, and install recreational and public access improvements (Texon Mill Park).

Recreational resources at the project include walking trails, picnic areas, fishing access, a canoe portage, and a visitor center. Public access is provided free of charge.

PLUS-Standard: The project owner voluntarily added the Texon Mill park and a fishway visitor center. The project has permitted camps on project land and funds a seasonal river ranger.