Just after 8:15 a.m., police received a call from a woman about a domestic incident at an address on Wynford Heights Crescent, located off Eglinton Avenue East and the Don Valley Parkway.
Police say a man left the scene in a black four-door vehicle, which he abandoned near the river.
According to police the man dropped something into the river, which they believe may be a firearm.
The man then got into the water on the eastern shore of the river.
The man was arrested on the west side of the river. He was taken to hospital shivering. The outside temperature at the time was about -15 C.
The man is in custody but there is no word on his condition or whether he will face charges.
Police are searching the area, but have not recovered a firearm from the scene.