Stonington ― For the fifth year in a row, the news is not good for the health of Wequetequock Cove, according to newly released data.

The Clean Up Sound and Harbors report card on the health of the Mystic River, Wequetequock Cove and other area waterways, which was released at its annual meeting Wednesday, gave the cove an “F” for 2022. It was the only waterway tested that received a grade less than a “C.”

“While we have seen improvements over the last 15 years in Mystic Harbor, more work is needed in the Mystic River and Wequetequock Cove,” University of Connecticut Professor Jamie Vaudrey, a marine scientist, told the crowd of nearly 100 gathered at the Thompson Exhibition Building at Mystic Seaport Museum.

This is the second time the cove has received a grade of “F” in the last five years and is down from a “D+” in 2021. For the 15 years of data contained in the report, the cove has generally received below 65%, or a grade of “D.”

The report also showed that the entrance to Stonington Harbor and Fishers Island Sound received “A’s,” and Mystic Harbor received an “A-,” though its northernmost test site, in Pequotsepos Cove, received a “D.”

CUSH bacterial sampling also showed Pequotsepos Cove often has high levels of fecal bacteria contamination, with levels exceeding allowable limits as much a 60% of the time, as did the northernmost testing site in the Mystic River, where Whitford Brook meets the river.

Though the report showed that Mystic River dropped from a “B” in 2021 to a “C” in 2022, Vaudrey noted the river’s water quality tends to vary and can be impacted by the weather such as drought or excess rain, or higher or lower-than-average temperatures. The lower score, though, is within the expected variability.

“This pattern tells a story of pollution and dilution in the Mystic area,” Vaudrey said, explaining that areas of higher population density lead to increased wastewater discharge from septic systems while having more pavement, roofs, and other hard surfaces increase storm water runoff which end up in waterways.

As the Mystic River widens into the harbor, contaminants are diluted by mixing with waters from Fishers Island Sound, but farther north, away from the flushing action of the Sound, water quality issues become more significant.

Unlike the river and harbor, Wequetequock Cove is flushed by water from Little Narragansett Bay, which, fed by the Pawcatuck River, also has water quality issues.

The health of Wequetequock Cove has been a source of concern for residents in the area, many of whom have found fecal coliform bacteria and other contaminants in their well water, while noting the degradation of the habitat and gradual loss of the former beauty and diversity of the cove.

Vaudrey explained that though water clarity in the cove is good, other indicators of marine health are quite poor, including oxygen saturation and levels of phytoplankton, which scored in the “D” range and levels of seaweed and dissolved oxygen falling.

Vaudrey recalled her visits to the cove in the early 2000s, saying that the cove was home to eel grass and healthy seaweeds like kelp but over time Cladophora -- a nutrient-loving seaweed that thrives on nitrogen pollution -- took over and, though it improves water clarity and supports phytoplankton, it is devastating for other marine life.

The seaweed has replaced other, healthy types of seaweed and has led to severely low levels of dissolved oxygen overnight during summer months which cannot support many types of marine life like the fish or the oysters that once populated the cove.

Vaudrey said the health of local waters can be improved, but sustained action and economic investment is needed to preserve and restore healthy, thriving waterways in the area.

“We have seen positive results in improved water quality resulting from investments such as sewage treatment upgrades and green infrastructure, therefore, we know that if we continue to commit the necessary resources and effort to the task, we will continue to make progress towards healthy conditions throughout our coastal waters — but it will require vigilance, persistence, and patience,” she concluded.