The Amazon River
Although there are people who have famously swam the length of the Amazon River, it’s important to understand that they did so at great personal risk. Some people assume that the presence of piranhas in the Amazon River’s waters is the biggest risk factor, but Rainforest Cruises noted that these fish have an overblown reputation for attacking humans and are primarily scavengers.
That having been said, they acknowledge that there are electric eels lurking in the depths of the river, and those are much more likely to have unpleasant encounters with humans. Furthermore, the Philippine Athletics Track and Field Association characterizes the river as featuring dangerously low visibility, bacterial and fungal growths, and strong currents during certain times of the year due to heavy rains.