Veterinarians usually get their college (bachelor's) degrees in something like biology or animal science. Then they go to vet school.All vets get a lot of the same training, but then they can specialize infields like marine animals. Are you interested in all sea animals, or just the mammals (whales, seals, otters, etc.)?

I checked out a site for people interested in working with marine mammals:

They suggest taking the following courses in high school: biology, chemistry, physics, mathematics, computer science, and language. It's important to study very hard and get good grades because so many people want to go to vet school that it's hard to get in.

You might also start looking around your area to see if there are volunteer opportunities for working with animals, even if they're not marine animals. This will help you decide whether you like the work or whether it is too hard, messy, or smelly for you.

When you are in high school and college, you can see if any marine animal organizations in your area have internship programs. Students at my college sometimes do internships with the sea lions at our county zoo.