Cameco has halted production at the Key Lake mill and activity has been reduced at the McArthur River mine.
The uranium mining company issued a statement on Sunday.
It says the disruption of operations is caused by the washout of the Smoothstone River Bridge.
The bridge is located on Highway 165 southeast of Pinehouse.
It is on the primary route used to transport supplies.
It is not known when repairs can be made and traffic returned to normal.