Thank you for the additional information.
Code 1 is a "normal" code, indicating that there are no detected problems in any of the systems that are monitored.
Right off the bat, I would suggest checking the air filter element to see if it got wet and is now restricting air flow. Reading in between the lines of your description of the problem, it will not achieve peak RPM's when in the water under load. A restricted air intake would be a possible cause for that. On the trailer, there is no load on the engine so it is always revs more freely on the trailer than in the water.
I would also suggest checking the oil to see if water got in it. Although that is not related to the performance issue you are experiencing, you certainly don't want to run the engine on diluted oil. There could also be a correlation between the crankcase being over filled with liquid now too. That would cause the crankshaft to be immersed in oil/water which creates hydraulic drag and can limit peak RPM's. Think about how hard it is to swing your fist under water and imagine that is what the crankshaft is trying to do inside the engine.
The next thing to do would be to remove and inspect the spark plugs. I would like you to describe what you see when you inspect them for me. What we would like to see is them all very similar in appearance. If one (or more) differ greatly from the others, please tell me, or better yet attach pictures of all the spark plugs.
Lets start there since the diagnostics do not indicate a component failure.