A river runs through it.

• Author: Morford, Stacy
• Position: Eye on Ecology - Hudson River

HOW'S THE WATER?--that is a question scientists often hear along the Hudson River. Can I swim or fish in the river? Will my kids get sick if they play in the water? There are good reasons to worry. The Hudson has a sordid past, and sections of it still frequently register fecal contamination levels many times beyond the limits considered safe for human recreational contact. However, there also are reasons for optimism.

A team of scientists working with the nonprofit Riverkeeper conducted an unprecedented health check of the entire river system, starting at the headwaters in the Adirondacks and going all the way to New York Harbor, where the river meets the ocean. Their results give the 315-mile-long Hudson River a mostly positive health report.

Marine biologist Andrew Juhl of Columbia University's Lamont-Doherty Earth Observatory and microbiologist Greg O'Mullan of Queens College took the northernmost point of the project, and arguably the most challenging: they hiked for two days up New York's highest peak (Mt. Marcy) to reach tiny Lake Tear of the Clouds, the source of the Hudson.

Riverkeeper, which celebrated its 50th anniversary in 2016, and Columbia have been partners on the river testing for the past 11 years, but this is the first year that scientists have gone to the source of the Hudson for testing.

Lake Tear of the Clouds is not much more than a shallow pond surrounded by pine forest, but the water is crystal clear. At one end, Feldspar Brook gurgles downhill on its way to becoming the Hudson. "When we collect samples farther south, we have what would naturally be in the river plus the signal of all the impacts from human activities along the way" Juhl says. "Up in the Adirondacks, we just have the natural signal, so it gives us a baseline for comparison."

The scientists' primary target for testing was Enterococcus, a bacteria carried by warm-blooded animals. In water, it is an indicator of fecal contamination, which can carry pathogens that make people who contact the water sick. Juhl and O'Mullan also tested the water's oxygen concentration, nutrients, temperature, pH, and turbidity, and they prepared samples for measuring chlorophyll to see how much algae was present and DNA sequencing to study the types of microorganisms found in the water.

The river has close to pristine conditions at its source, with no detectable Enterococcus. Downstream, near an old iron mine site from the 1800s, the scientists detected Enterococcus at...