That's a good point about invasive species. Being a nearly exclusive saltwater paddler, it didn't occur to me. I can't remember the last time that I paddled two different fresh water bodies consecutively.

The rot issue does affect canvas skins as you pointed out, but the bigger issue is frame rot. Fresh water promotes it, saltwater prevents it. Depending on the wood(s) chosen for the frame, this can be a serious concern. The point is that if you have the option it's best not to do a fresh water rinse of a boat that's been used in saltwater. If I end up with significant sand or other foreign material in an SOF, I'll rinse it with saltwater before loading it on the car. I do the same with fiberglass boats and have never had a problem with them.