Dressing in a pastel blue, coral pink, mint green, etc. is preferable to give off an ocean-vibe. It needs to seem like you're part of the ocean. No one would spare you a glance if you dress as everyone else which completely defeats the point of standing out.
Wait, why can't you join us on the swim team again?
Fish are friends, not food. Harming sea animals is completely horrifying, especially being a fish yourself! Kind of. You need to show a close relationship with fish, proving you are one of them to people, even favoring fish over them. Treat them as a real friend, smile kindly, wave when appropriate and such.
You've Convinced Them!
You cannot be seen wet at all. Make a big deal about it in public when there are people around. Do not overreact so much it's obnoxious, you just want to grab attention and curiosity. For example, when a splash of water gets on you in a classroom, don't say anything. Stand up fast, maybe even make your chair clatter on the floor and sprint out of there, no questions asked.
Absurd excuses are a sure way to confuse people and have them thinking about you afterwards.