Emergency crews were in the process of pulling a body from the Rideau River at Brewer Park near Bronson and Riverside Drive early Thursday evening.
A canoeist noticed the body and reported it to police Thursday afternoon.
Few details were immediately available on the case.
Meanwhile, rescue crews were busy for most of the day with another search on the Ottawa River after two people reported hearing cries for help early Thursday morning.
Ottawa police say two passersby were walking on the Alexandria Bridge when they heard someone screaming, "Help, I can't swim" at about 1:20 a.m. Thursday.
Firefighters from both sides of the river searched the area with thermal imaging equipment overnight, but didn't find anything.
Ottawa police took over the search during the day. Marine units were sent out and air and ground searches were also launched.
Police say they found what they call an "entry point" under the Alexandria Bridge on the Ontario side of the river where it looks like someone went into the water.
Police won't confirm reports that a trail of blood was found near the bridge.
With files from CTV Ottawa's Catherine Lathem
