I'm sorry, but first of all, these are extremely biased pictures; you haven't really captured just how cool the oceans are, instead focusing on some rather unappealing details; you can find just as disgusting pictures for freshwater and pictures of saltwater just as beautiful as those that you posted of freshwater.
I'm sure that you're love for freshwater comes from the fact that you have events in them, but, seriously, oceanography can be monumentally more interesting. Trust me. I did freshwater Dynamic Planet last year (regionals, states, and nationals); and it is not nearly as interesting as oceanography. There are simply so much more to oceanography (as expected; they kinda cover 97% of the Earth's water), from more interesting physical phenomena (waves, tides, eddies, currents, tsunamies, turbidity currents, etc. as opposed to downcutting, waterfall recession, and other freshwater phenomena) to more interesting life (think about all of the types of saltwater fish vs. the types of freshwater fish; there really is no comparison in terms of how many more types of saltwater fish there are.) and more. If you are fortunate enough to do Oceanography as a Science Olympiad event, and attack the event as enthusiastically as you have done with Freshwater Dynamic Planet, I'm sure that you will come to the same conclusion.
Before you go and assert that one thing is definitely better than another, it would do you good to know a significant amount about both, not just the one you support.