to help every one here, and you, I would say where abouts you lost your boat.
No one boats below filter plant here, and if you lost it in the farmlands between the mouth of the canyon and fort collins your best bet is to start hiking the river from where you swam and move down stream.
Any people who might grab your boat off the bike path by sheilds might not return it, so start looking asap.
Was it a rental, or does it have your info in it? I am sorry you lost your boat, im only trying to help, but id say the best chance of recovering it from the river is to go look for it. If I see it, I will let you know.