STONY BROOK, N.Y. (AP)  -- A new study finds that mercury in Hudson River fish has declined strongly over the past three decades.

The study _ done by professors at Long Island's Stony Brook University _ notes efforts by activist groups, government and industry to help clean up the river system.

Researchers examined the mercury levels of fish collected over much of the Hudson, from New York City to the Adirondack watershed.

They say mercury that has been found seems to come from a source upstream _ perhaps from the Adirondack watershed or an industrial source.

The fish examined include striped bass, yellow perch, bass and carp.

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