Rash on my stomach that is raised red patches almost like red bumps, but are more patchy. began after running by river & city water got weird smell.

Superficial skin: infection? Strange that not entering the water or river could give you enough contact or exsposure to cause enough irritation on the skin to start infection. Or maybe this was a chemical irritant? But then you would think it should also be on any exposed skin. You need to see if it clears on it's own. An OTC steriod cream might help.