The Nechako Reservoir, sometimes called the Ootsa Lake Reservoir, is a hydroelectric reservoir in British Columbia, Canada that was formed by the Kenney Dam making a diversion of the Nechako River through a 16-km intake tunnel in the Kitimat Ranges of the Coast Mountains to the 890 MW Kemano Generating Station at sea level at Kemano to service the then-new Alcan aluminum smelter at Kitimat. When it was constructed on the Nechako River in 1952, it resulted in the relocation of over 75 families. It was one of the biggest reservoirs built in Canada until the completion of the Columbia Treaty Dams and the W.A.C. Bennett Dam that created Lake Williston. The water level may swing 10 feet between 2790 and 2800 feet.

The damming "linked the rivers and lakes of Ootsa, Intata, Whitesail, Chelaslie, Tetachuck, Tahtsa and Natalkuz into the reservoir with a surface area of over 90,000 hectares." "The water of these lakes and rivers was diverted westward to the Pacific Ocean, instead of eastward to the Fraser River."

The creation of the reservoir flooded the series of lakes which typified the upper Nechako basin and in the process rendered the Quanchus Range, which lies between the north and south arms of the reservoir, a virtual island. The names of lakes amalgamated into the reservoir are perpetuated as names for the various stretches of water. The north arm includes Ootsa Lake, Whitesail Lake, and Whitesail Reach, the south arm Eutsuk Lake, Natalkuz Lake, Chedakuz Arm, Knewstubb Lake, Tetachuck Lake and others. Because Ootsa Lake is the largest of the original lakes its name is sometimes used for the whole reservoir, though the official name remains Nechako Reservoir.

Tweedsmuir North Provincial Park and Protected Area and Entiako Provincial Park both border the reservoir.

For many generations, the shores of Ootsa Lake were home to the Cheslatta Carrier Nation. The flooding of Nechako Canyon destroyed their traditional hunting and fishing grounds and their homes.

In the late 1940s, University of British Columbia professor Charles Edward Borden shifted his attention toward urgent salvage archaeology in the Nechako Canyon after learning that ALCAN planned on flooding the Nechako Canyon to supply power for their smelter in Kitimat (known as Kemano I Project). In 1951 Borden and his protégé, anthropology student, Wilson Duff located over 130 sites of importance to Cheslatta T'en history. They conducted more intensive investigations prior to the flooding of the area. The damming triggered "devastating changes for First Nations communities whose traditional territories lay in their path, including the destruction of Aboriginal gravesites, territories, livelihoods, and archaeological sites." In 1957, Alcan opened the gate of the spillway to Skin's Lake desecrating Cheslatta graves, which came to public attention during the Royal Commission on Aboriginal Peoples.

In the 1970s, Alcan proposed expanding the generating capacity at their Kemano Powerhouse by diverting more water from the Nechako Reservoir. At that time, it was envisioned that no additional dams would be required, and there would be no additional flooding. However, the project faced challenges and was ultimately canceled by the Provincial Government in 1995 due to significant environmental concerns related to the Nechako River.

Recent developments indicate that efforts were made to address the energy needs while considering environmental impacts. A second power tunnel between the reservoir and the powerhouse was planned for this purpose. It was intended to serve as a backup to the original tunnel, enhancing the sustainability of the project. In December 2017, there was a significant development when the US-$473 million Kemano second tunnel project received the go-ahead, as reported by the Kitimat Northern Sentinel. This project likely aimed to improve the efficiency and reliability of power generation while mitigating environmental impacts, in line with contemporary environmental standards and regulations.

However, the completion date for this project was scheduled for 2020, according to available information.

The "out-of-date" template remains in place to indicate the need for further updates and verification of the project's status beyond May 2023.

Tahtsa Lake is at the far western end of Nechako Reservoir and has a subarctic climate (Köppen Dfc), with high levels of precipitation and snowfall.

Wistaria is on the northern shore of Nechako Reservoir, about 85km east of Tahtsa Lake. Wistaria also has a subarctic climate (Köppen Dfc), but it receives far less precipitation and snowfall.

• List of lakes of British Columbia
• List of tributaries of the Fraser River
• Kenney Dam

• "Nechako Reservoir". BC Geographical Names.
• Christensen, Bev (1995), Too Good to be True: Alcan's Kemano Completion Project, Talonbooks
• "Ootsa Lake-Nechako Reservoir", Heritage British Columbia, 2009
• Neuberger, Richard (1951), Engineers Invade Another Wilderness - Huge Canadian Power Project Marks 20th Century Frontier Boom, Popular Science, retrieved 3 December 2013 Detailed and illustrated Popular Science article on the Kemano Hydro Project.\
• Roy, Susan (October 2010), These Mysterious People Shaping History and Archaeology in a Northwest Coast Community, McGill/Queen's University Press, p. 240, ISBN 9780773537217
• Christensen, Bev (1995), Too Good to be True: Alcan's Kemano Completion Project, Talonbooks

• Neuberger, Richard (1951), Engineers Invade Another Wilderness - Huge Canadian Power Project Marks 20th Century Frontier Boom, Popular Science Detailed and illustrated Popular Science article on the Kemano Hydro Project