Is a platypus considered a marine animal?

Ok I'm doing a science project and I want to do it on a platypus it has to be a marine animal and I think marine means ocean but a platypus doesn't live in an ocean it lives in fresh water so is it not a marine mammal? I know that we can do a penguin and there semi aquatic just like the platypus but penguin are by the ocean and salt water and a platypus is by fresh water so my question is is can a platypus be considered a marine animal?