If you were wondering whether or not the oceans in existing worlds can be made routable for Sims to swim in, it’s “unlikely”. SimGuruDaniel took to Twitter yesterday to state that they would most likely have to create new terrain/worlds for that specific purpose.
If making current ocean terrain routable is not something that can be done, then it’s very likely our Sims will only be able to swim in the ocean in specially made worlds.