MATTAPOISETT — Mattapoisett resident Louis Casi is originally from the island of Martinique. He was one of about three dozen who swam Monday, Dec. 25 at Mattapoisett Town Beach in support of Helping Hands and Hooves, a local nonprofit that provides therapeutic horseback riding lessons for adults with disabilities.

The water wasn’t as cold as Casi was expecting, he said, but it was cold enough. And as someone from the Carribean, “it’s different,” Casi said.

It was about 30 degrees when the swimmers ran quickly in and out of the water. The rule was participants had to go all the way in — including their heads.

“If the tide was a little higher it would be even better, but it was excellent,” Casi said.

Casi has been swimming in the Christmas Day plunge with Helping Hands and Hooves for five years, he said.

This was the 21st year of the swim, according to Helping Hands and Hooves co-founder Debbi Dyson.

“Every time I enjoy it very much,” Casi said. “It’s for a good cause.”

A few thousand dollars are usually raised for the nonprofit each swim, according to Dyson.

She and fellow co-founder Julie Craig also partake in the plunge.

“You can’t ask people to and then not do it yourself,” Dyson said.

“The only way you get out of it is if you're deathly ill,” Craig said.

Another pair of participants, Mattapoisett residents Dominic and Doreen Philie, said — expectedly — the water was cold.

There’s “a cold shock the second you hit the water,” Dominic Philie, 12, said.

“It’s a good charity, so we wanted to come and support them,” Doreen Philie said.

Dyson said one year they had to shovel a path to the water through snow. That wasn’t the case this year, but the temperature was subfreezing.

Craig said the worst part of the plunge is one’s feet running out to the swim. There’s rocks in the water, and the feet go numb pretty quickly, she said.

“That part is tough, but it’s fun,” Craig said. “It’s invigorating.”