I missed this one, it played during Shark Week last summer. Sounds like a bombastic blockbusting blast of blood and mayhem. Short plot blurb, polar ice caps melt and the world is just ocean, due to some aberration, there are no fish for the sharks to eat, they must feed on surface dwellers. Basically Waterworld meets Jaws.
The original Planet of the… Movie. Planet of the Apes!
Another honourable mention Shark Movie: