The environmental group Riverkeeper's annual Hudson River report shows many locations still fail to meet federal guidelines for safe swimming.
The report released Thursday says sewage pollution will continue to be a problem without new regulations, enforcement, and investments in infrastructure.
Riverkeeper samples 74 locations between New York Harbor and Waterford monthly from May to October in collaboration with scientists at CUNY Queens College and Columbia University's Lamont Doherty Earth Observatory.
It tests dozens more locations in Hudson River tributaries in partnership with citizen scientists.
The report says 23 percent of Riverkeeper's samples failed safe-swimming guidelines.
Rainfall makes it three times as likely that an area will have sewage pollution.
And certain tributaries are more contaminated than the river, acting as pollution sources.
Water quality data is available on Riverkeeper's website.