The swimmers, some in elaborate costumes, gathered at Goose Lake in Anchorage for the annual fundraiser.
A part of the ice was cut away, allowing swimmers space for a dive, a cannonball or even a timid step into the freezing water.
David Aromin, who came from Philadelphia to take part, said he had happily braved the 0C water temperature for “a great cause”.
“I’m new to Alaska and this is one way to be baptised,” he added.
Special Olympics Alaska president Jim Balamaci said the fundraiser, which was running for the eighth year, brought in more than $300,000.
Mr Balamaci and his team run a year-round sports training and athletic competition for children and adults with intellectual disabilities.
He added: “When you have a thousand athletes coming out on one of the shortest days of the year, in the middle of winter, to jump into 32 degrees (farenheit), to say: ‘You know what? We’re just going to unite our communities, we’re going to accept everybody and we’re going to do this all together’, it just warms my heart.”