The "Notebook" star jumped at the chance to be a part of directors Michelle Dougherty and Daniel Hinerfeld's hard-hitting film after they sent her a rough cut of the project, reported People magazine.
"I was shocked by it and very emotional and surprised about how little I knew about what's going on in our oceans. You don't hear it, but it's a whole cacophony down there.
"The idea that a baby whale couldn't find its mum because they communicate through sound is so sad. And not only whales, but a lot of marine life - even shrimp - depend on their hearing," she said.
And McAdams, 37, hopes the movie will inspire change.
"We need to have these species around us forever or for as long as we can. This noise pollution is pushing a lot of them to the brink.