Travel along Highway 72 toward Sioux Lookout has been cut off.
The Ministry of Transportation says it is due to flooding.
There are reports that a beaver dam broke, causing water to cover both sides of the highway about five kilometres north of Dinorwic.
The highway between Dinorwic and Highway 664 is closed until repairs can be made.
There is no word on how long the highway will be closed.
Travellers wanting to reach Sioux Lookout will have to take Highways 599 near Ignace and Highway 642 at Silver Dollar.