For 20 years, Dennis Chillemi has been swimming the Hudson River. That's nothing unusual for the Tarrytown resident, who began swimming in the river as a child, mostly at the old beach at Kingsland Point Park. But for these last two decades, his dips have been much further — and for a deeper purpose.

Chillemi, the executive director of the Leukemia and Lymphoma Society (LLS) of Westchester, is one of the founders of the Annual Hudson River Swim For Life, which takes place today, in an amended form.

Due to health and safety concerns, swimmers and kayakers will complete a one-mile swim along the shores of Sleepy Hollow instead of the traditional three-mile route from Nyack to Kingsland Point Park in Sleepy Hollow.

It's a far cry from Chillemi's first swim. "It was literally just me, and I swam from Piermont to Irvington," he says. The original plan was to swim from Nyack to Tarrytown but, "the winds were bad that day."

When he climbed out of the water, his wife said, "if you're going to do this, you should do it for a charity," says Chillemi, the father of seven.

The next year, a half dozen people joined him and they donated the proceeds from their efforts to Blythedale Children's Hospital; the next year, there were 18, then 20.

Chillemi, who still does the swim, was expecting nearly 400 people, but that number may be smaller due to the safety alert. It's also traditionally the largest kayaking event on the Hudson. Last year's event raised more than $260,000 with proceeds going to LLS.

Some participants swim just for the challenge, but most of them do it for the mission. "They know someone or have a connection to someone with a blood cancer," Chillemi says. Swimmers come from Canada, Florida and across the metropolitan area. "It's a unique event," Chillemi says. "Open water swimming across the Hudson is a challenge. When people come and do this for the first time, it's quite literally a life-altering experience."

It also changes the lives of those suffering from leukemia or lymphoma.

This year's swim pays tribute to Julia Pierce, a Harriman resident who was diagnosed with acute lymphoblastic leukemia at the age of 4. Julia underwent chemotherapy for 27 months at Maria Fareri Children's Hospital. Now 7 years old and in first grade, Julia is in remission and has been off chemo for several months.

"Julia is a living example of the sobering reality that every four minutes in this country someone is diagnosed with blood cancer," says Chillemi.

Even if you don't swim, you can still participate on shore: there will be entertainment, food and a bone marrow donation held at Kingsland Point Park.

"There has never been a better time to come together to celebrate the Hudson, while at the same time help others with blood cancers," Chillemi says.