NANJING, Dec. 11 (Xinhua) -- When Wang Jianbei furtively burrowed through hills for quarries 15 years ago, he never expected to become a major player in the environmental sector one day.

The 53-year-old is now adept at directing unmanned boats to detect water samples in Tianmu Lake, the only potable water source in his hometown of Liyang, a small city in east China's Jiangsu Province, located in the lower reaches of the Yangtze River.

In 2005, Wang established a building materials plant and made his first pot of gold in no time. The exorbitant profits from this business lured his footprints into more quarries in the quest for more raw materials.

But the factory generated massive pollution, too. It emitted dust into the air and discharged industrial effluent into Tianmu Lake, posing a health hazard to local residents and incurring frequent complaints.

"I feel guilty for polluting the environment," Wang admitted.

Wang's factory was, however, just the tip of the iceberg in the Liyang area, where mine and quarry exploitation had started to thrive since the 1970s. The building materials sector had been the pillar industry of the city for quite some time.

With China putting greater emphasis on green and high-quality development in recent years, the once fiery, grubby industries began to cool down.

By the end of 2019, Liyang had shut down more than 190 quarries and brickkilns, restored over 50 scarred mines and spent 3 billion yuan (about 459 million U.S. dollars) on pollution and sewage treatment.

As a result, the water quality of Tianmu Lake has reached the national Level II standard, the second-highest in the five-grade ranking system.

In the wake of the environmental protection efforts, Wang closed his factory in 2013 and started an unmanned boat production company two years later. Such boats are widely used in environmental monitoring, oceanographic survey and rescue operations.

Earlier, despite making money, Wang said, he was gripped by a feeling of disgrace for undermining the environment. "But, seeing the water in Tianmu Lake become clear I am relieved now."

Liyang has embraced a different development model, aiming to forge "all-for-one" tourism as the city's new identity.

Liyang unveiled a beautiful "rainbow road" in 2017, linking 86 administrative villages. It brought the lesser-known rural areas to the tourism fore and also encouraged farmers along the road to take up jobs in the tourism sector.

The "rainbow road" has helped more than 100,000 farmers increase income, official data showed. Meanwhile, leisure agriculture and rural tourism in Liyang saw more than 8 million visits last year, raking in 4 billion yuan.

As a small city by the Yangtze River, Liyang offers a window into the green growth and high-quality transformation of the Yangtze River Economic Belt, which covers nine provinces and two municipalities, accounting for more than 40 percent of the country's population and economic aggregate.

China's leaders have promoted the high-quality development of the Yangtze River Economic Belt, calling for prioritizing ecological conservation and boosting green development.