Be nice. We are here to do good things, not to fight.
We usually include a moderately long pedal as part of our day. Sometimes it is at the beginning before we start work or sometimes it is split between going out and returning. It's generally somewhere between 4 and 5 miles total. Your upper leg muscles are the largest in your body and this gives you a decent cardiovascular workout.
During the couple of hours we spend picking up line and litter the rear position does all of the paddling and maneuvering. This is moderately strenuous and builds upper body strength. Though the bowrider does not get this benefit, they do get the mental part.
Sun exposure causes the body to produce Vitamin D, a crucial vitamin. It is the only really natural way to get as much as your body needs.
Time spent outdoors has been shown to significantly improve your mental health. You can read this article or this study for more details.
Hunting for and retrieving fishing line is a relatively simple task that requires focus and concentration. This clears your mind of the noise that is usually up there and gives you a feeling of peace. I understand that this is similar to Zen, though I'm not knowledgeable about that.
And then there's the wonderful feeling you get when you spend time removing hazards from the environment of birds and wildlife. Of knowing that you have physically made the world just a little bit better than it was.