"Do I need a model release?"
This is the answer you should get any time you ask that question:
"What are you planning to do with the photo?"
I'm not an attorney. Find a grain of salt and take it with my advice.
To own the photo, you never need a model release.
To sell copies of the photo, you MAY need a model release for any featured people in the photo. It depends on where the photo was taken and the circumstances surrounding the shot. This particular photo would not fit such a description.
To sell the photo to a newspaper for editorial purposes, you often do not need a model release. This photo would need none.
To use this photo to advertise Ontario, boats, or an inn... No, because these people were not asked/hired by you to row out there. Thus, no one can identify exactly who these people were. If you staged this shot, they'll know that they're in the shot and you should get a release.
To sell this photo, copyright and all, to a stock agency, perhaps... No, but don't "indemnify" the purchaser of the photo against claims.