By the time he walks into his Market Street office at 8 a.m., Jamie Patrick, 40, has been up for hours, swimming in an Endless Pool in his garage. For lunch, the general manager of his family’s office supply firm Patrick & Co. hits up Aquatic Park or Golden Gate Tennis & Swim Club for another 90 minutes in the water. Come the weekend, he’s freestyling in the bay. It’s all part of his training to swim the length of the Sacramento River next month to raise money for Buena Vista Auxiliary’s literacy programs in Contra Costa County. He’ll start at the bottom of the Lake Shasta dam and plans to swim 240 miles nonstop over nearly three days in 55- to 72-degree water to reach Sacramento. If he succeeds, he’ll break the record for the longest GPS-confirmed, non-wetsuit river swim in the U.S.

Save for floating snack breaks and the occasional thumbs-up from his safety crew in a boat, that’s a lot of time alone with his thoughts. “In open water, you don’t have any visual stimulation,” says Patrick. “It’s dark, cold, but peaceful listening to the water. You’re all in your mind. It’s almost meditative.”

But he’s had some practice with that. Born in San Leandro, Patrick began swimming competitively at age 7 and continued through high school and college, followed by 18 years of triathlons, 15 Ironmans, and a couple of Ultramans. “I was racing myself into shape,” he says. These days, Patrick is focused on water marathons. Last summer, he became the first person to double-cross Lake Tahoe, from Incline Village in Nevada to Camp Richardson on the California side and back—all told 44 miles in 25 hours.

Patrick figures his Sacramento River marathon should take 60 to 65 hours to complete. In the meantime, he’s practicing in Northern California open waters—Lake Berryessa (13 miles), Clear Lake (18 miles), and from San Francisco to Alcatraz (2 miles)—to keep him from getting bored with logging training time. “Those sea lions in the bay? They are not friendly,” says Patrick. “You can’t see anything in the water, and all of a sudden they pop up in your face. Honestly, I’m a little afraid of them.”