Cai is a keen swimmer. In the past, Dongdawan was ideal for the sport due to its open and flat sands.
"The situation worsened to us coming across garbage every few meters in the water. I feel disgusted when I think of dangerous fishing nets in the sea. Our children swam there," he said.
Coastal communities had long dumped their waste into the sea because of a lack of garbage disposal plants.
"In recent years a burgeoning fishing industry has resulted in much more garbage, yet the people here have not changed the way they dispose of it," he said.
"It is an insult to leave the beach littered with refuse. I had to do something for my motherland."
Cai's wife, Chen Shenghua, 64, has been his supporter and partner. Both are in good physical shape. While Cai heads a community winter swimming organization, Chen leads the local tai chi association.
With the help of volunteers from these clubs, the couple led their first coastal cleanup in July 2014.
"Plastic bags, drinks bottles, dead fish and mice. You'd be surprised what can come in from the ocean. At the beginning we would collect about 20 metric tons each day," Cai said.
"Refuse above the sand was just the tip for the iceberg. We soon moved to using a digging machine for garbage that had been buried for years."
Cai recalled how locals would come and stare at him working stripped to the waist. In response, he would shout "It's our beach" and call on them to pitch in.
In 2015, Cai established a beach protection volunteer association. The organization now has about 240 members ages 20 to 80.
Over the years, he has led more than 500 cleanup activities and removed over 740 tons of garbage. The group has also started on other beaches in the county.
Efforts at building environmental awareness have certainly been successful.
"All the garbage buried in the sand has been removed. These days in Dongdawan you never see anyone dump anything. People feel ashamed when they see so many devoted to conservation," he said.
"But our work can never end because ocean currents will always be washing garbage in. The steps of our volunteers will continue with the rise and ebb."
Gazing down at the shore, which is today a much prettier site than when he started his work, he smiled.
"You see," Cai said, "when the tide is out, egrets fly down on the beach searching for food."
