Top 3 Largest Lakes in Montana

Montana's largest lakes are dominated by reservoirs on the Missouri River system and one massive natural lake.

1. Flathead Lake — 189 sq mi (490 km²). Natural glacial lake (Flathead River). Clear, cold, 113 m max depth. West shore: Flathead Indian Reservation; east: orchards, cherry country. Largest natural freshwater lake west of Mississippi by surface area.
2. Lake Koocanusa — 92.6 sq mi (240 km²). Reservoir behind Libby Dam (Kootenai River). 145 km long; extends into British Columbia (68 km in Canada). "Koo-can-usa" = Kootenai + Canada + USA.
3. Fort Peck Lake — 88.7 sq mi (230 km²). Reservoir behind Fort Peck Dam (Missouri River). 2,100 km shoreline (longer than California coast). Largest by volume in Montana (24 km³). Part of Charles M. Russell NWR.

Honorable Mentions

• Canyon Ferry Lake (35 sq mi) — Missouri River.
• Hungry Horse Reservoir (34 sq mi) — South Fork Flathead.
• Lake Elwell (Tiber Reservoir) (26 sq mi) — Marias River.

All are major recreation hubs (fishing, boating, camping) and critical for irrigation, flood control, and hydropower.