But there's one thing he loves just as much as spending time on the banks of the Mississippi: planting trees.
"Trees are a great thing for the environment," said Pregracke, the CNN Hero of the Year in 2013. "It has a lasting impact."
So, in 2007, he and his nonprofit, Living Lands & Waters, set a new goal: to plant 1 million oak trees in communities across the country.
This morning, the organization reached this major milestone.
"There are a million trees planted out there," Pregracke said. "It's a really big deal. We probably have 800,000 different families watching those trees grow up, and I think it's really impactful and really cool ... like leaving a legacy."
Pregracke and his group surprised elementary students in Port Byron, Illinois, by planting the millionth tree at their school.
Highlights of the ceremony included an 11-foot walking "Treeman" and Pregracke's speech to the students, which carried a message about setting goals.
"This goal of a million trees is a very big goal," he said. "I'm just a regular person, but it's always good to set big goals and keep working really hard and take all the small steps to achieve something big."
To date, more than 95,000 volunteers have helped Pregracke and his group remove 8.7 million pounds of trash from the nation's waterways.
"The new goal," Pregracke said. "We'll just plant another million!"
Want to get involved? Check out the Living Lands & Waters website and see how to help.
For 10 years, Dan Wallrath has been surprising wounded veterans with homes of their own.
His nonprofit, Operation Finally Home, provides custom-built houses to injured service members and their families, mortgage-free.
Last month, the group celebrated its 100th home.
"It all started out with (CNN Heroes) recognizing us, and it took off from there," said Wallrath, who was honored as a Top 10 CNN Hero in 2010. "We've changed the lives of (the) families because of it. Now you've got 100 families where their kids can possibly go to college; 100 families with dads ... relieved of financial pressure."
Operation Finally Home works with local builders, contractors and developers nationwide to design the homes to meet the veterans' needs. The homes have an average market value of $300,000.
On April 14, in a special dedication ceremony in League City, Texas, the group presented the keys for its 100th home to U.S. Marine Corps Cpl. Jonathan Dowdell and his family. Dowdell is a double amputee who was injured while serving in Afghanistan.
For Wallrath, the group's recent accomplishment only makes him want to do more.
"Our next goal is to build 100 homes a year," he said. "I know it's a lofty goal, but we're going to try. Unfortunately, we're going to ... have more men and women with catastrophic injuries, and we're going to have to be there to help them."
Wallrath believes the next 100 is right around the corner. The group currently has more than 80 homes under construction in 31 states.
Want to get involved? Check out the Operation Finally Home website and see how to help.
Ten years ago, Andrea Ivory started knocking on doors.
The breast cancer survivor wanted to help spread the word of early detection to underserved women in her Miami, Florida, community.
Today, her grassroots effort is 10,000 volunteers strong. They've knocked on more than 88,000 doors. And their message has grown.
"Because heart disease is the leading cause of death for women -- 400,000 women die every year from heart disease -- we've taken a step further in our approach," said Ivory, a Top 10 CNN Hero in 2009. "We're not just focusing on early detection, but prevention."
Her group -- now the Women's Breast & Heart Initiative -- today reaches women in three counties: Miami-Dade, Broward and Palm Beach.
"Breaking down barriers, that's what we do -- by bringing the services into the neighborhoods," Ivory said.
The group's community screening and wellness events provide mammograms as well as hypertension, glucose and cholesterol screenings. Participants engage in physical activity and receive a healthy eating guide and fresh fruits and vegetables.
"We foster change by teaching women and giving women the tools to make healthy lifestyle choices," Ivory said.
Ultimately, Ivory hopes to take the program's success and replicate it across the country, starting by expanding throughout Florida in the next five years.
"When you have an opportunity to shape and change a life for good, it draws you in. It draws me in," Ivory said. "I want to change the world."
She and her group will celebrate the 10th anniversary of their grassroots efforts with a special event this weekend.
Want to get involved? Check out the Women's Breast & Heart Initiative website and see how to help.