[ganeumann]

This is true of many riverfront municipalities. 771 cities in the US have combined sewer overflows [1]. My partner monitors the pollution level in the Hudson across from NYC (in Hoboken) and when it hasn't rained in a few days the water is clean enough to swim. But after a heavy rain, it is, indeed, foul.

That said, the Hudson is ridiculously cleaner than it was 20 years ago. So much so that the Marine Borer (a type of worm that eats wood) has made its return and is destroying the old piles that hold up parts of the landfill on the waterfront. Unintended consequences, but worth it.

[1] List here: http://water.epa.gov/polwaste/npdes/cso/