The St. Clair Region Conservation Authority expects some flooding in the Sydenham River watershed on Thursday.
Rain over the last 36 hours has kept water levels high.
The conservation authority says water levels are expected to peak in the East Sydenham River at Dresden until Thursday night and Bear Creek at Brigden by Thursday afternoon.
People are being urged to stay away from rivers and streams because of slippery banks and fast flowing water.
The warning is in effect until Friday.