To pollute a river requires only one flush of sewage from homes or factories, but the recovery process can take dozens of years.

A local resident, surnamed Chen, grew up near Donghu Lake, a drainage basin in the Changle district of Fuzhou, capital city of Fujian province.

"The water in the lake was very clear with fish living in it when I was a little kid. The water could even be used for drinking," Chen said.

But in the following years, the water quality gradually deteriorated because of livestock waste, village garbage and illegal discharging of sewage in the lake.

The lake's once crystal-clear water turned dark and smelly. Water hyacinth on the lake once covered more than half the surface and eventually the water couldn't be used for farmland irrigation anymore.

Since 2013, the local government has invested 420 million yuan ($60.6 million) to restore the lake.

"We shut down 250 livestock farms surrounding the basin, laid 13.3 kilometers of sewage-collecting pipes connecting 120 factories and dredged 5.33 km of waterways," said Wang Jianbo, press spokesman at the Fuzhou environmental protection bureau.

"We dredged streams and brooks to the lake, built slopes at the banks and built paved trails and greenbelts in the upper reaches of the basin," Wang said.

There is also a pump station close to the lake used for pumping sewage to a nearby disposal plant.

"Finally, Donghu Lake has returned to what it looked like 30 years ago," Chen said.

After two years, the recovery project was completed and the water quality has improved significantly.

As a result of the improvement, Donghu Lake hosted a national kayaking competition in October 2015.

Various plants grow along the water's edge, including Manila grass, willow trees, Chinese banyan trees and eucalyptus.

Over the next few years, the environmental protection bureau will monitor the factories and livestock farms along the lake and improve the sewage systems in neighboring areas to make sure raw sewage is dealt with properly, according to Wang.

Donghu Lake's example reflects Fuzhou's efforts in recovering polluted rivers in the city.

The city government recently released a comprehensive plan for managing the urban water system.

It proposed that pollution control should be carried out from the four perspectives: water-logging management, pollution source control, treatment of polluted water and environmental recovery for surrounding waters.