At midnight, Tom Casavant dove into the 68-degree waters of the Pacific Ocean.

Thirteen hours later, a little after 1 p.m., he stumbled onto Point Vicente beach in Los Angeles, completing a task only a handful of athletes have been able to accomplish — swimming the 21.5 miles from Catalina Island to Los Angeles.

Casavant, 56, a professor of electrical and computer engineering at the University of Iowa, swam the distance on Aug. 19 — in 12 hours, 59 minutes and 19 seconds.

“I was absolutely happy to finish,” he said. “I was really prepared to take as long as it took.”

The channel between Santa Catalina Island and Los Angeles is the only crossing on the American continent that compares to the English Channel in both distance and difficulty, according to the Catalina Channel Swimming Federation.

Casavant said he decided to attempt the swim about two years ago. He applied in March.

After passing a medical examination and other requirements — including an eight-hour swim and an additional four-hour night swim in Lake Macbride — be became one of the nearly 50 people the Catalina Channel Swimming Federation accepted to attempt the feat.

Karen Casavant, 56, Casavant’s wife and a physical therapist assistant at Progressive Rehabilitation Associates, and eight family members and friends made up Casavant’s support crew.

The support crew accompanied Casavant during the swim, and a crew member in a kayak gave him hourly nourishment.

Casavant said he expected the physical challenge because this was the farthest and the longest he’s ever swum.

However, he said, the hardest parts were the mental challenges. Toward the end of the swim, he was demoralized.

“It was close to seven hours, and I just had a lot of pain in my shoulders,” Casavant said. “I just started thinking ‘I’m not going to make it.’ This was the first time in my life that I was doing something this difficult that I thought I would have to quit. I was at my limit.”

Karen Casavant, as well as other support crew members, encouraged him to keep going.

“He was seeing the same scenery because he was in a current that was against him,” Karen Casavant said. “He wasn’t making very good distance for a long time — less than a mile an hour. So every time he looked up, it looked the same.”

Casavant said he was able to focus on finishing and just “swim as hard as I can until I get there or I just can’t go any farther.”

Only about 400 swimmers have completed the solo swim in almost 90 years. The first individual to complete the swim was George Young, of Canada, on Jan. 15, 1927, in about 16 hours.

A relay team first swam the channel Sept. 10, 1926, according to the federation. Since then, more than 100 relay teams have succeeded in the swim.

The channel is far from Tom Casavant’s first challenge. On top of weekly swims in Lake Macbride, he has completed swims across the world, including in the Indian Ocean and off the coast of Australia.

Although he began competitive swimming when he was 8 years old, Casavant said he started open-water swimming when he was challenged by his daughter, Kayla, to compete in a race in Lake Harriet in Minneapolis in 2012. He has been swimming in open water ever since.

“I think one of the really appealing things about open water swimming is that it is different,” Casavant said. “It’s not a very controlled environment — nature and whatever conditions are that day — that’s a part of it.”

And even though the Catalina Channel is his peak accomplishment, he said, he has no plans to quit open-water swimming anytime soon.