To make a meaningful difference you’d have to add so much salt that swimming just wouldn’t be fun anymore. Never mind the utter infeasibility of it all in the first place:

Add salt to lakes, kill every living thing in and around the lake, deal with an enormous amount of rotting bio matter, and probably poison drinking water for an entire ecosystem.

Add it to pools, deal with salt deposits everywhere that ruin all the pool equipment, and make the water so saline that you can’t dump it anywhere.