There are over 35,000 scientific peer-reviewed papers in respected journals regarding bacteria in the (salty) ocean. There's no way I'm going to list all of those here. In this paper, they isolated 519 different strains of bacteria looking for those that might be antibacterial (which sounds crazy, given they are bacteria, but they mean where one strain of bacteria produces substances that inhibit/kill many other strains) and there is also this paper regarding fecal bacteria in coastal wetlands. As for viruses, salts kills some, such as H1N1 as described in this paper, but not others as described in this paper, this paper, this paper, this book and many others. Perhaps you should buy the book Oceans and Health:: Pathogens in the Marine Environment.

Look at the CDC Surveillance Summaries for Waterborne Disease and Outbreaks which show outbreaks in recreational water including marine water and in fact in all untreated water where the outbreaks have varied sources whereas treated sources (i.e. chlorinated water) had mostly the protozoan oocyst Cryptosporidium parvum which is why the CDC Model Aquatic Health Code (MAHC) is looking at requiring UV or ozone in new/modified commercial/public pools.

A critical point that is being missed, however, is the volume of water. Oceans have a very large volume so when you swim in them the fecal bacteria that you shed get diluted greatly. The same is true in large lakes and in flowing rivers. Even so, people still get sick in such water venues. However, swimming pools are very different in that they are much lower volume and are mostly static. The fecal bacteria you shed, as well as the viruses and protozoan oocysts (if you are sick) all go into a much smaller volume of water where the bacteria can reproduce at will and the other pathogens survive until they find another host (i.e. swimmer). Salty water is not sufficient to kill or inactivate such pathogens and certainly not to do so quickly enough to prevent person-to-person transmission of disease. Remember that human body fluids already are at around 9000 ppm salt and that many of early microorganisms came from the sea so have mechanisms for dealing with salt.

And then there's the impracticality of having very high salt levels in swimming pools with the attendant metal corrosion issues, stinging eyes (do you open your eyes underwater in the ocean?) and killing of plant life and contamination of waste water treatment plants for inland locations whenever you backwash or otherwise replace the water.

I believe your idea needs a little more thought.