Why is the Hudson River so green?

Just like land-based plants, phytoplankton contain chlorophyll—a green pigment essential for plants to conduct photosynthesis—which is currently evident in the color of our waters. The Park regularly monitors the river for different water quality indicators, including plankton diversity and abundance.



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The Mississippi River This once pristine waterway is perhaps the most polluted in the United States. Part of the problem stems from agriculture. The Mississippi River traverses much of America's heartland, drawing no end of runoff from factory farms. Animal waste isn't the only problem.

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According to the New York State Department of Environmental Conservation (NYSDEC), there are no known incidents of sharks in the Hudson River. However, there is always the potential for sharks to be present in any body of water, so it is important to be aware of potential risks when swimming in the river.

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Predators like blue crabs and sturgeons do eat zebra mussels, but have never been shown to control natural populations. Research on new control measures, including biological controls, is ongoing, but the changes we've seen to the Hudson's ecosystem probably are irreversible or at least long-lasting.

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Surveys in 1957 found the river was unable to sustain life, and the River Thames was eventually declared “biologically dead”.

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