The Interlake Formation is a stratigraphical unit of Silurian age in the Western Canadian Sedimentary Basin.

It takes the name from the Interlake Region in Manitoba, and was first described in outcrop by A.D. Baillie in 1951.

[2] The Interlake Formation is composed of very finely crystalline dolomite.

The Interlake Formation is present throughout the Williston Basin.

[1] It reaches a maximum thickness of 335 metres (1,100 ft) in the subsurface of North Dakota, and is typically up to 110 metres (360 ft) thick in outcrop in its type locality.