IAAEE. Since sea water is a very good conductor, you would be hard pressed to put "30MW of into the sea." Assuming these are generating at 13.8 kV, and they somehow had their lineside terminals dunked in sea water, you would get a lot of noise and steam followed by the generator protection relays kicking in in like a cycle and a half. Call it 25 ms. The excitation to the generators would be shut off and the voltage would quickly dwindle. You'd have a bunch of fucked up equipment, and anybody in the immediate area might be exposed to electrocution and arc flash hazards, but there wouldn't be noticeable impact to the rest of the ocean. Hell, the generator itself would probably be OK.
Short circuit calculations are something that any power generation place deals with all the time. When you are shorted, you get a lot of current, but not a lot of volts, so your power will go down substantially. Just like when you accidentally drop a screwdriver across a battery. You get a spark, damage the battery, maybe take out some ESD sensitive components, but by and large the rest of the components on the board are OK. There's just no way for the energy to get out to the rest of the world.
In order to get 30MW of electricity actually into the sea water, well... I'm not exactly sure how you could do it. This sounds like a job for Randall Munroe, honestly. You'd probably have to only dunk one phase in the drink. Then you could at least get a little time before the ground fault and unbalanced load relays kick in. You could run the sea water through very long PVC pipes, essentially turning the water into a 30MW heater, and that would raise the temperature of the water. But that's not exactly what you have in mind. Besides, that's sort of like what other power plants do with their waste heat. They dump it into a cooling water body, although not quite at that level you're talking about.