Groton — The annual New Year’s Day run and swim here brings a group of runners who have become close friends over the years for a good, noncompetitive event that ends with a plunge into the usually frigid waters of Long Island Sound.

Wednesday’s run and swim was all of that, but with a somewhat more somber tone added, as the hundreds of runners and supporters also turned their thoughts to the upcoming April 21 Boston Marathon. Last April, terrorist bombings killed three people and injured 264, disrupting the festive atmosphere that surrounds the race.

Former American marathon record-holder Patti Dillon of New London, who finished second in Boston three times, rallied local runners Wednesday to contribute to a worldwide effort to pen messages for the bombing victims that will be presented at the starting line April 21.

As runners gathered early outside St. Mark’s Episcopal Church on Pearl Street in Mystic, Dillon encouraged them to sign the 6-by-18-foot canvas banner that will be Connecticut’s contribution to the banner effort. Dillon also had brought the banner to her church, Calvary Chapel in Uncasville, for members to sign.

“God’s peace be with you,” the Colemans wrote.

“Thoughts and prayers,” wrote Bonnie and the girls.

“Be strong. You will be fine,” someone wrote. “Sending love from Connecticut.”

Dillon then brought the banner to the finish at Esker Point Beach, where dozens of family members and friends bearing the towels and blankets the runners-swimmers would need after their plunge. Dillon figured she’d better collect signatures and messages before the runners arrived. She was right.

The beach scene quickly erupted in chaos with cheers and screams as the runners arrived, kicked off their shoes, sloshed through the frozen seaweed and dived or splashed into the low-tide water.

Colin Kuntz, 19, of West Hartford, was perhaps first to the water’s edge, but as he bent to remove his shoes, others beat him into the water. He still wore a broad smile as his pale skin turned red after his full-dive plunge.

“Help me!” screamed several girls in the Holland and Austin families of Ledyard as they emerged from the 47-degree water. Eight sisters and friends in the two families have made the run-swim event an annual New Year’s Day tradition.

Older sister Jennie Austin was content to bear the towels for Liz, 17, and Julia, 14, and their friends Bethany, 20, Abbey, 14, and Michaela Holland, 18.

“Ahh!” Jennie Austin said, hugging her cold, wet sisters and friends. “You’re crazy!”

Jim Roy, 53, of Mystic stood on the bathhouse deck taking in the scene after his brief swim. Roy has participated in most of these New Year’s Day events since 1978 and helps organize it each year. Roy is active with the John Kelley Memorial Fund which is raising money to erect a life-sized bronze statue of the late Boston Marathon winner in the small park next to Mystic Pizza. For many years the New Year’s Day event began at Kelley’s house on Pequot Avenue.

Roy said he loves the atmosphere of the event. The run is low-key and non-competitive, and running friends get to reunite after months or even a full year of not seeing one another.

He also appreciated the community support. Groton Town police stopped in at the beach and patrolled the run route. Groton’s Parks and Recreation Department opened the bathhouse for swimmers to change into dry clothes.

And the swimmers weren’t the only ones in the water. Fifteen kayakers from the Connecticut Sea Kayakers, Inc. — affectionately calling themselves “Connyakers” — paddled through West Cove on the lookout for swimmers who might be in trouble. Kayaker Phil Warner of Hamden, Mass., has made the New Year’s Day trek to the Groton shoreline for the past 13 years.

“It’s better than New Year’s Eve,” Roy said. “It really is a great tradition. It’s a wonderful event.”

c.bessette@theday.com