Waterproof boxes aren't truly water-proof, but that's better than exposed outlets.
Having electrical outlets over open water is risky, and if you can do anything to reduce that risk, I think it's worth it. Water can make contact a variety of ways: A pump squirting upward, a big splash when you drop something or when livestock decides to jump, or even during something mundane like a waterchange and the hose accidentally floods our outlets as you move it from point A to point B. On top of that, salty air occurs around the clock due to evaporation, and when the climate calls for it, condensation can occur on and in those outlets. Has any of this struck a chord with you? Think about how your electrical is currenlty set up, and if you know something needs doing, don't delay. Saltwater and electricity often equals fire, and that means loss of life and property.