I've always suspected natural is better, even when it comes to swimming... I have debated this over and over with my aunt Isabelita who often recall her childhood memories bereft of swimming at the Sto. Tomas river - spanning from the Cordillera hills to the South China Sea. I often tell her those were the best swimming experiences I had - ever.
Now that people from around the world identify the wonders of how nature works, such as Biotop, I am now bolder at declaring the possibilities of swimming with other biological creatures on the same area without much harm done on the person.