Researchers from Columbia University take water samples from the Hudson River. View Full Caption Columbia University

UPPER WEST SIDE — The Hudson River attracts thousands of swimmers and kayakers each year — along with antibiotic-resistant bacteria, a new study found.

After testing water samples from 10 spots on the Hudson's estuary between Westchester County and Lower Manhattan, scientists found that 38 percent of microbes were resistant to tetracycline and 84 percent were resistant to ampicillin — drugs used to treat ear infections, pneumonia and more.

Antibiotic-resistant bacteria are particularly dangerous for people with weakened immune systems, according to scientists at Columbia University's Lamont-Doherty Earth Observatory, who co-authored the study in the Journal of Water and Health.

This isn’t the first time antibiotic-resistant bacteria have been found in the river, but this is the first study to make the connection between the microbes and the untreated sewage that regularly flows into the Hudson River, the scientists said.

The strongest presence of antibiotic-resistant bacteria came from samples with the most sewage-indicating bacteria. Some of the estuary's top offenders included parts of Flushing Bay, as well as areas near the sewage outfall pipe at West 125th Street.

According to the study, more than 27 billion gallons of raw sewage and rainwater are released into the Hudson each year by wastewater treatment plants, often through combined sewer overflow after heavy rains.

The announcement about the scientists' findings came just days after thousands of swimmers plunged into the Hudson River for the Aquaphor New York City Triathlon. The 1,500-meter swimming race took place just below the sewage outfall pipe at 125th Street on July 14.

John Korff, one of the triathlon's organizers, said he was skeptical of the study because of the Hudson's shifting nature, and he believed the Hudson was safe to swim.

Because it is a tidal river, its water can flow in different directions on different days. On any given day, samples could pass safety inspections in one part of the river and fail in another depending on myriad circumstances, he said.

"We hear stuff all the time," he said. "People say, 'I heard I need a tetanus shot,' or 'the Loch Ness monster is in [the Hudson]'...or 'I heard they found a body part.'"

Organizers rely on the Department of Environmental Protection's assessments of the Hudson's water quality in determining whether to hold the swim leg of their race.

"It's all about the safety of the athletes," Korff said. "There is no middle ground."

And the Hudson is cleaner now than it has been in the past.

Richard Beeson moved to West 87th Street in 1970, when the lack of sewage infrastructure made the river smell putrid.

“There were no ducks, no geese. No one was fishing,” he said. “It has improved markedly.”

However, he and his wife, Ellie Fry, regular visitors to Riverside Park, still have no plans to go for a dip in the river.

“I [still] wouldn’t get near the water in any way, shape or form,” he said.