Another week, another mixed bag when it comes to water quality for Long Island bays, harbors, rivers and inlets.

As of this week's sampling, 12 out of 29 shore locations were rated good, meaning clear water, adequate oxygen levels and no or low levels of algae and/or bacteria from human or animal waste, making for hospitable conditions for fish and shellfish. Eleven sites were rated fair, and six, poor.

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.

Once again, water quality readings this week were mixed, he said.

Conditions found at the poor sites — the Peconic River, Forge River, central Great South Bay, Mattituck Inlet, Western Flanders Bay and Three Mile Harbor — included algal blooms, some harmful; low levels of oxygen and water clarity; and with some locations also seeing elevated levels of fecal bacteria.

In addition, that central area of the Great South Bay “continues to experience a harmful algal bloom of chattonella, along with near-zero oxygen levels at night, and poor water clarity,” the report said.

Temperatures in South Shore bays were found to have risen to the low 80s, the warmest of the season so far, he said.

Seawater at such high temperatures “naturally holds less oxygen,” and it takes just “a slight disturbance in the natural balance of the ecosystem for oxygen levels to get dangerously low at night,” Gobler said.

Chattonella, rarely found around Long Island, has potential to be a fish-killer and, given the densities found through the sampling, could be having a negative impact on “resident fish populations.” It’s not toxic or any danger to humans.

Since the water quality project was 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, finally, shorter days mean less oxygen 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.

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,” Gobler said.

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