Why are you so gullible to such fanciful explanations? First, only 1% (approx) of all freshwater and marine life is diadromous (i.e., can live in either freshwater or saltwater at some point in their lives, e.g., salmon). The remaining saltwater fish will often experience some form of Osmotic shock if the saline content drops significantly compared to their local environment. Some saltfish can survive only at certain depths, temperatures, salinity content, etc. There's no way that all saltwater fish can survive in the same salinity content as all freshwater fish. Every saltwater fish specialist knows this. If you doubt it, go to your city's local Aquarium and ask them.
In addition, there's no way that coral can survive freshwater conditions. This is why coral doesn't grow in the Great Lakes, for example. Too bad they don't, coral can beautify the water (just go to Bora Bora in the Tahiti chain to see how beautiful the water is there). In any case, if a flood of fresh water de-salinated the water near corals (i.e., near land continents), all those corals would immediately die (killing about 25% of the saltwater population).
You really need to stop thinking along this pseudo-scientific line of reasoning. You are 18 now, no longer a kid like Sam. He still has a year or two to entertain children dreams about fantasy possibilities of the past. You are now an adult and must take on more responsibility for your thoughts. You don't have time to fantasize about crazy ideas having absolutely no possibility of being true. Perhaps I say too much, but you guys are still young enough that you can correct your mold of thinking to be very reasonable and rational adults. Unfortunately a number of young people grow up in conditions where ridiculous notions are not addressed immediately and with proper sound responses, and therefore they become immune to sound reasoning as they age. At some point, a point that varies on each individual, human adults often become unwilling to entertain concepts that don't agree with their pre-conceived beliefs (which are often religious or philosophical beliefs). At that point, it is almost hopeless to reason with them (hence, creationist 'science'). You guys don't see that because all you see are college degrees and what appears to be equal credentials with honest-to-good evolutionary scientists.
In any case, you guys might have already passed that point. The only thing that reasonable people can do is try to make you think, but more importantly it is to show others how irrational these pseudo-scientific ideas actually are.
Warm regards, Harv