The Finlay River is a 402 km long river in north-central British Columbia flowing north and thence south from Thutade Lake in the Omineca Mountains to Williston Lake, the impounded waters of the Peace River formed by the completion of the W.A.C. Bennett Dam in 1968. Prior to this, the Finlay joined with the Parsnip River to form the Peace. The headwaters of the Finlay at Thutade Lake are considered the ultimate source of the Mackenzie River. Deserters Canyon is located just north of Williston Lake.