The risk of flooding is currently greatest downriver from the nation's capital, according to the Ottawa River Regulation Secretariat.
Michael Sarich, chief engineer with the secretariat, says that has to do with where the rain is falling and the melting of the snowpack.
"[The water will rise] a little bit later above Ottawa, but below Ottawa — because the tributaries are very close to the river, particularly on the Quebec side, with a lot of snow — things are coming up very quickly," Sarich told CBC Radio's In Town And Out on Saturday.
"It's going to be peaking into Monday [and] upstream a little bit later."
While flood levels are not projected to hit 2017 levels yet, Sarich said that may change as temperatures rise and cause the snowpack to melt faster upstream.
Record-breaking levels possible
In downstream communities like Clarence-Rockland, Ont., volunteers have been working hard to prepare homes and other properties for potential floods.
Other towns like Rigaud, Que., have reported minor flooding, with residents there already being urged to pack up and leave their homes.
Sarich is warning that water level records could be broken for some of the Ottawa River's tributaries.
"The Mississippi is probably going to break a record for this time of the year. Not sure what it's going to do in terms of an overall peak, but it's still rising," Sarich said.
Sarich is asking people to remain alert as conditions could change rapidly along the river.
In Ottawa, city officials have said they expect levels on the river to peak on Tuesday.