Ocean waters do hold gold, but it's difficult to say exactly how much. If you were hoping make your fortune mining the sea, consider this: Gold in the ocean is so dilute that its concentration is very small. One study found there is only about one gram of gold for every 100 million metric tons of ocean water in the Atlantic and north Pacific.
There is also (undissolved) gold in/on the seafloor. The ocean, however, is deep, meaning that gold deposits are a mile or two underwater. And once you reach the ocean floor, you’ll find that gold deposits are also encased in rock that must be mined through. Not easy. Currently, there is no a cost-effective way to mine or extract gold from the ocean to make a profit.