Is there an issues with enough oxygen dissolved in oceans, lakes, rivers to keep marine life alive?

There can be, and lakes or ponds tend to suffer it the worst because of size, but even the ocean has large "dead zones" where the oxygen has been depleted. A big problem is the presence of nutrients that cause plants to thrive, which you would think would add oxygen, and it does. but when the plants die and sink and start to decay, they consume oxygen. Zones with too much organic debris (life remains) can easily get depleted in dissolved oxygen.

Some places are naturally depleted, like the bottom of the Black Sea, but human activity has created a lot of new problem areas.

Yes ,sometimes there ate issues with that. Periodically the oxygen at the moths of the Mississippi river become so oxygen depleted that Gish and I shrimp and scallops and clams die. The water becomes anoxic. This means the people who depend on seafood don't make any money.

There can be. There was recently a big fish kill in the Darling River due to oxygen depletion following an algal bloom.

Yes there is. It's a lot to explain in detail. Because of the oxygen depletion, much of marine wildlife are adapting and moving to different locations. Most of this is due to climate change.