The Lakehead Region Conservation Authority has upgraded its flood outlook statement to a flood watch.
Communities affected include Thunder Bay, Neebing, Oliver Paipoonge, Shuniah and the townships of O`Connor, Conmee, Gillies and Dorion.
Rainfall in excess of 50 millimetres expected to fall on Sunday, with the number rising if thunderstorms hit.
The warning cautions residents to be careful around area waterways and remove stored items next to banks to higher ground.
Parents are also reminded to keep children away from all waterways.
The LRCA says it issues flood warning when conditions indicate the potential for flooding exists. It remains in effect until Tuesday.