The body was pulled out of the river by the Alexander Docks, downstream from where police dive teams had been searching for Gibson, 32.
Police began looking for Gibson after her infant son and two-year-old daughter were found critically injured in the family home Wednesday morning. The children were rushed to hospital where they later died.
On Thursday, police said they thought Gibson was still alive. But they turned their attention to the Assiniboine River near the family's home Friday after exhaustive searches of parks and the riverbank in the Westwood neighbourhood.
Police were alerted to the body in the Red River Saturday morning after it was spotted by someone in the area. The Alexander Docks are just downstream from where the Assiniboine and Red Rivers meet up.
Police spokesman Const. Eric Hofley told CBC News police were unable to confirm the gender of the body immediately and likely would not be confirming identity on Saturday.