IDNLearn.com: Your go-to resource for finding expert answers. Get the information you need from our community of experts, who provide detailed and trustworthy answers.
Answer: It would be ocean's
Explanation: In this context the apostrophe show ownership, or WHOSE waters became choppy (I know an ocean is a WHAT and not a WHO but phrasing it like this in my mind always helped me). Without the apostrophe it would be the plural form of OCEAN.