Stonington — The seaweed problem plaguing sections of Little Narragansett Bay for the past several years has spread to new areas this summer, prompting a renewed effort by environmental groups and local leaders to brainstorm possible solutions.

“It’s getting worse,” Sally Cogan, secretary of Clean Up Stonington Harbors and head of its water quality monitoring program, said Tuesday.

“There have been times at Elihu Island where the whole island is surrounded 20 feet out (with seaweed) to the point where we can’t swim and can’t paddle a boat out because we get stuck,” she said.

The type of seaweed taking over the bay is cladophora, which is growing rapidly due to high nutrient levels in the bay, poor tidal flushing and warming waters due to climate change, said Jamie Vaudrey, assistant research professor in the Marine Sciences Department at the University of Connecticut’s Avery Point campus in Groton.

“It’s expanding and is everywhere in Little Narragansett Bay,” Vaudrey said. “It’s ousted everything else out of the bay.”

At 4:30 p.m. Wednesday at the Mason’s Island Yacht Club, Vaudrey and other experts from UConn will explain the causes to an invited group of about 20 people, including leaders of residents’ groups, environmental groups and town leaders.

The group plans to visit nearby Elihu Island to see the problem firsthand.

“I’ll explain the dynamics of why we’re getting this seaweed bloom,” Vaudrey said.

There may be no quick fix to the problem, she said, “but if no action is taken now, it’s going to keep getting worse.”

The meeting will be a continuation of efforts begun by Stonington resident Karen McGee, who founded the Coalition for the Management of Seaweed in Stonington Borough in 2014 after thick mats of cladophora made the Ash Street Beach near her house unusable.

A long-term solution has not yet been found, she said.

Last week, David Prescott, South County Coastkeeper for Save the Bay, saw the largest floating mat of the algae he’s seen in the past 10 years while doing water quality testing.

It was covering a large area of the surface between Barn Island and the east side of Sandy Point Island.

“It was really hard to navigate through,” he said. “It had floated to the surface while it was decaying, and was decomposing and foul-smelling.”

With the spread of cladophora, the biodiversity of plant and animal species in the bay is declining rapidly, he said.

“We need to work at the sources of this,” he said.

The meeting is intended to educate local leaders about the problem and develop an action plan, he said.

Vaudrey said analysis by one of her graduate students has determined that about 30 percent of the nutrients fueling the growth are coming from discharges from the Westerly and Pawcatuck sewage treatment plants.

Both plants discharge nitrogen-rich effluent into the lower river.

Kenyon Industries, a fabric-finishing plant on the river in Kenyon, R.I., also is contributing, Vaudrey said.

Discharges from homes and businesses on the river with septic systems are adding about 15 percent of the nutrients, and another 37 percent is coming from fertilizers that run off from farms and lawns throughout the large watershed.

The remainder is coming from nitrogen-rich rain and dust particles settling out of the atmosphere onto the land, then washing into the river, Vaudrey said.

She believes a public education campaign is needed to encourage residents and business owners to curtail fertilizer use throughout the Pawcatuck River watershed, which extends into more than 300 square miles into 14 towns in Rhode Island and Connecticut.

In addition, upgrades to the municipal sewage treatment plants could also reduce nitrogen inputs, she said.

Cogan said a flow study is needed to determine how the tides and currents are moving through the bay.

Fran Hoffman, a member of Clean Up Stonington Harbors's board of directors, said she hopes the meeting will encourage town leaders to further their efforts to adopt organic land use practices for athletic fields, parks and other town properties.

First Selectman Rob Simmons said he hopes to attend the meeting to learn about the problem “and see if something reasonable can be done.”

But any solution, he added, will require the cooperation of the towns on the Rhode Island and Connecticut sides of the river.

j.benson@theday.com