The Hudson was notorious decades ago for being tainted by everything from industrial chemicals to old tires and sewer runoff. Even as late as 2004, when Swain swam the length of the river to encourage its continued cleanup, a New York Post headline read: Love That Dirty Water; Eco-Nut Swims The Slimy Hudson River.

The caution regarding swimming in the Hudson River stems from a long history of industrial pollution and modern sewage concerns. For much of the 20th century, the river was contaminated with PCBs (polychlorinated biphenyls) dumped by manufacturing plants, leading to it being designated as one of the largest Superfund sites in the U.S. While the water is cleaner today than it has been in a century, people are still warned against swimming in certain areas, especially after heavy rainfall. This is due to Combined Sewer Overflows (CSOs), where storm runoff overwhelms local systems and sends raw sewage into the river, spiking bacteria levels (like E. coli). In 2026, it is a high-value strategy to only swim at officially sanctioned spots like Croton Point Beach or Kingston Point, where the water is tested regularly. Swimming elsewhere, particularly near NYC, is discouraged because of heavy vessel traffic and the risk of swallowing water containing lingering toxins or pathogens.