I'm not really clear on carrying on the water. I had a buddy that got his CCW the same time I did. He was launching his dads boat, while they were together. Some one spotted his carry piece in its holster. That person got freaked and called a Ranger over or some thing. The officer approached my friend, asked him about his piece and if he was carrying. My friend said it was for snakes, water moccasins, which are very aggressive around here. The officer agreed, and said as long as he didn't here TSHTF, he would leave my friend alone.
I have looked over MO CC laws many times, but I have not seen anything regarding carrying on the water. I guess it could depend on what govt agency controls the body of water. State parks, Army corps of engineers, water in a national park(policy is changing), etc. Could be different for each. Dont know. Could be banned/covered under the "any where specificlly prohibited by fed law".