Water quality as of the latest sampling was deemed a mixed bag for Long Island bays, harbors, rivers and inlets, with six out of 29 locations found to be poor.

Out of the shore spots sampled on Monday, 13 got good ratings, meaning clear water, no or low levels of algae and/or bacteria from human or animal waste, and hospitable conditions for fish and shellfish. Ten were rated fair.

That’s according to the Long Island Water Quality Report, a weekly score card issued from Memorial Day to Labor Day. It’s created by Chris Gobler, professor of marine science at Stony Brook University and director of the New York State Center for Clean Water Technology, and his team of more than 20 students and scientists.

“Water quality is mixed across Long Island,” he said.

Among the conditions found at the poor sites were dense harmful algal blooms in Hempstead Harbor, Northport Harbor, Forge River and the Meetinghouse Creek area and nighttime oxygen levels approaching zero for central and eastern Moriches Bay. Other factors included low water clarity and the elevated levels of fecal bacteria.

Since the water quality project launched in 2014, the team has picked up on how water quality tends to morph as the summer progresses.

Over the years, “we've learned that oxygen levels are high and good in June, but declined through July and August, sometimes to levels dangerously low for marine life,” Gobler said.

Three factors are at play, he said. As waters warm up, we get “the cumulative growth of algae over the summer,” warmer water holds less oxygen, and shorter days mean less of it is produced, Gobler said.

The aim of the weekly water-sampling project is to provide regular snapshots of ecosystem health, with an eye to how well locations are supporting — or not supporting — robust fishing and shellfishing activity.

While the beach crowd may find some basics useful — water temperature and clarity assessments — this is not the place to go to see what locations are up to snuff for swimming and splashing around. Look, instead, to official calls from county health departments on where to swim or not, Gobler said. And, for any curtailment of shellfishing, the state Department of Environmental Conservation is the go-to official source.

Sampling is done on Mondays, as six teams “fan out across Long Island, collecting water samples, making measurements, and downloading data from logging devices, like oxygen meters,” he said.

From all that, the good, fair and poor scores are determined.

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