Yang said he is not well educated, but he understands one principle: If you live near the ocean, you must protect it because you rely on it to raise your family.

A study published by Science in 2015 estimated that 8 million tons of plastic waste are dumped in the ocean each year. Plastic waste affects marine wildlife such as sea birds and fish, which can become entangled or choked by it.

Yang said the water surrounding the Shengsi Islands was crystal blue 20 years ago. However, swarms of tourists and overdevelopment of its coastline posed a serious risk to local marine ecology.

"If the situation had continued, the fish and shrimp would have disappeared one day. A trash-collecting ship was what we needed most," he said.

But local shipbuilding workshops did not know how to build the ship he wanted, so Yang had to design it himself.

"If it's too big, it cannot enter the harbor; if it's too small, it can't resist strong wind and waves," said Yang, who changed his design many times.

After the Canghai No 9 was built, Yang employed three crew members to clean up the waters within a 90-kilometer radius of the Shengsi Islands.

The ship goes to sea every day except when there is extreme weather or the crew is on leave.

His expenses amount to at least 700,000 yuan a year for the crew's wages, fuel and maintenance fees.

"It's big money," Yang said. He has set himself a target - to collect trash in the ocean for another 10 years, as long as he can afford it.

China has adopted a string of measures to ease environmental strain, ranging from coral restoration campaigns and clamping down on illegal wastewater discharge to treating polluted rivers and launching public education activities.

It's difficult to find a good way to collect and manage the garbage in the ocean, he said.

"Encouraging people to throw their trash into the right place is the most important thing," Yang said.