China has experienced fast economic development over the past four decades, but that also has put a lot of pressure on its environment. This is particularly true for cities relying heavily on natural resources. In today's special series, our reporter Liu Xinqing went to San Men Xia, a city along the Yellow River, which used to be famous for its rich reserves of minerals, but now is choosing a different path by turning itself into a "city of swans".

Swan Lake Wetland Park -- A heaven for swans -- Right at the turn of the Yellow River. Every winter, tens of thousands of white swans flock to the Yellow River Wetland in Sanmenxia, to escape the cold in the north, making it a "city of swans". Lu Chang'an has been working at the park for six years. For him, feeding the swans every morning in the winter has become a daily routine.

LU CHANG'AN STAFF, SWAN LAKE WETLAND PARK "We start at seven every morning. Each island normally gets 300 to 400 kilograms of corns. We provide about 2000 kilograms of corn to these swans each day."

Over the past decade, Sanmenxia has been built into a national-level Forest City with a forest coverage rate above 50 percent. It has become a major habitat for these elegant birds throughout winter -- a change felt at every corner.

LU CHANG'AN STAFF, SWAN LAKE WETLAND PARK "As the environment has kept improving, the number of swans has also kept increasing over the past years. Both the government and residents here are very aware of contributing to a good environment. This lake alone hosts about 6,000 swans; the neighboring lake has almost the same number."

But the "city of swans" did not come about easily.

LIU XINQING SANMENXIA, HENAN "White swans are very sensitive to air and water quality, and only choose to stay in the best places. The fact that more and more of them are attracted to Sanmenxia city during their annual migration says a lot about the environment here. It's hard to imagine that this city used to be an industrial center."

WANG FENGJIE DEPUTY DIRECTOR, SANMENXIA DEVELOPMENT AND REFORM COMMISSION "We have built a resource-based city by relying on rich reserve in natural resources. These industries did bring us glory in the past, but at the same time, caused a lot of environmental challenges."

As China strives to change to a more ecological path, cities like Sanmenxia are trying to find ways to transform their industries. Natural resources are still very important to the city's development, but now in a different way.

WANG FENGJIE DEPUTY DIRECTOR, SANMENXIA DEVELOPMENT AND REFORM COMMISSION "We have pushed industrial enterprises to change by closing down smaller, polluting factories, and encouraged larger enterprises to transform from raw material processing to high-end manufacturing and move up the value chain."

China long ago realized the negative environmental impact from economic development and has been stepping on the brake to stop industrial pollution. But fixing a damaged environment could be costly.

ZHANG ZHONGLIANG DEPUTY DIRECTOR, SANMENXIA ENVIRONMENTAL PROTECTION BUREAU "We have invested more than five billion yuan in environmental infrastructure, pollution controls and phasing out outdated industries for cleaner production."

So while Sanmenxia still has an industrial base supporting its economy, it has reached harmony between man and nature -- a much-needed blueprint for China's future development. Changes always come at a cost, but in Sanmenxia's case, it's been proven well-worth it. LIU XINQING, CGTN, Sanmenxia, Henan province.