Ottawa's mayor declared a state of emergency in the Canadian capital in anticipation of rising flood waters and heavy rains.
No homes have been evacuated, but authorities expect waters along the Ottawa River to rise above levels in 2017 that saw the worst floods in Eastern Canada in half a century.
Environment Canada issued a special weather statement predicting up to 35 millimetres (1.3 inches) of rain by Saturday morning.
Together with the snowmelt that feeds the river, waters are expected to rise up to 11 centimetres (4.3 inches) above peak levels reached in May 2017.
In addition to assistance from the province of Ontario with management of the emergency situation, some 400 troops will be deployed on Friday to key areas to help fill sandbags.
"We can no longer do it alone," Ottawa Mayor Jim Watson told a news conference.
"We are now beyond our city's capacity, and that is why we have called in the armed forces."