The view under the George Washington Bridge was just one of many milestones for John Henkelman, a PhD student who has spent the past month canoeing the Hudson River from its headwaters in the Adirondacks to New York City.

On Sunday, he capped his 315-mile trip in Manhattan.

Henkelman, 38, who studies natural resource management at the University of New Hampshire, combined his background in chemical testing with a passion for paddling to investigate the Hudson’s health and challenge a common belief.

“Everybody that isn’t a paddler thinks that the water is the dirtiest thing in the world,” he said. “So far, all of my tests have been clean.”

Armed with tools to measure nitrates, phosphates, dissolved oxygen and carbon dioxide — “what I like to call river vital signs,” as he put it — Henke

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