Along with the Milk River and Big Muddy Creek, it is one of three waterways in Canada that drain into the Gulf of Mexico.

West Poplar River rises near Killdeer, Saskatchewan, and flows south-east, into north-eastern Montana, past Richland and across Daniels County.

It is 9.9 m (32 ft) high, was built in 1957, and is owned and operated by the Saskatchewan Water Security Agency.

[7] Poplar River (Middle fork) rises north-west of Rockglen, Saskatchewan, and flows south-east, into north-eastern Montana, and passes west of Scobey.

[9] Girard Creek, which originates at Fife Lake, and East Poplar River are the primary inflows for the Morrison Dam Reservoir.