Paddleboarding/kayaking & the exercise ring

[Suggs68]

I wore my Watch while kayaking in the ocean today. Paddled for about 3 miles at a pretty good clip. The exercise ring barely showed any exercise, showing only 4 minutes when I was paddling for over an hour. When I run without using the watch's exercise app, it shows the amount of exercise pretty accurately. Anyone know why it doesn't recognize paddling as exercise?
And FWIW, after cleaning the salt water off the Watch when I got home, it looks as good as new.

 

[Bigeric23]

I"m guessing it doesn't detect enough movement or elevation in heart rate.