Photo by Linda HeronPhoto Credit

Little Long Generating Station, Mattagami River

The Lower Mattagami Project is a hydroelectric project that includes the addition of a new third generating unit to the existing two-unit Little Long Generating Station.

Existing Facility

The existing Little Long facility includes two vertical propeller turbine-generator sets, penstocks and draft tubes, and three existing single-phase transformers. Little Long has been in-service since the mid-1960’s.

Located 80 km north of Kapuskasing, Ontario, the facility is operated remotely from OPG’s Northeast Control Centre located at the Porcupine Transformer Station in Timmins, Ontario.


The expansion includes one vertical propeller turbine-generator set, penstocks and draft tubes, and one new three-phase transformer. The addition of the new generating unit adds 66.5 MW to the existing capacity for a total site capacity of 203.5 MW at a head of 26.5 metres.

As part of the expansion, a tailrace gate hoisting system is installed on the existing powerhouse tailrace deck, extending over the new tailrace deck of the powerhouse extension.

Water from the Mattagami River is conveyed from the existing Little Long GS intake structure for the third generator unit to the new spiral case via a concrete encased steel penstock.

Water from the new generating unit is returned to the Mattagami River via the existing 800 metres long tailrace canal.

The new generating unit is installed at the existing concrete structure. All three generating units share the same gravity dam and powerhouse.

The new generating unit is connected to Hydro One’s 230kV H22D circuit at the Little Long GS switchyard.

Location: Mowbray Township, Ontario
River System: Mattagami River
Nameplate Capacity: 203.5 MW
OPA Contracted Capacity: 203.5 MW
Operator: Ontario Power Generation
Technology: Hydroelectric
Turbines: Three vertical propeller turbines
Originally Built: Mid-1960’s
Coordinate: 50° 00’ 17” N, 82° 09’ 55” W
Project Progress (December 31, 2013)

  • Work focused on operational testing of the new unit in preparation for commissioning in Q1 2014

Ontario Power Generation Inc.