Do you think marine life might develop intelligence to rival humans?

If there were a waterworld in a habitable zone, and it remained constant for sufficient time, how likely do you think it is that intelligent marine life would develop? Is it likely that such intelligent marine life may evolve in Earth’s waters?

By intelligent, I mean equal to or better than stone-age humans, able to contemplate changes in the environment and use intelligence, migration, tools, construction and the like to adapt to such changes. Some sea life on earth, cephalopods for example, are learning rudimentary tool use and can solve complex problems. How smart can they get?