There is a magical lush green forest in Songshan Lake where animals have made their homes, but it is not easy for people to find it, as it is underwater of the Yanling Wetland.

In the Yanling Wetland, a 1.6-kilometre-long and 1.6-meter-deep scenic river is crystal clear, with patches of "foxtails" swaying gently in the water, which is truly beautiful.

"The top of this submerged plant is like a fluffy foxtail. It is Myriophyllum spicata, a pioneer species in the ecological management of water. They were planted three years ago," Wu Pengju, vice director of the Dongguan Municipal Ecological Environmental Protection Research Institute and doctor of ecology, introduced.

In addition to Myriophyllum spicatum, the underwater forest also has Nuphar pumilum with golden yellow flowers. The water's transparency is so high that one can spot fish swimming in groups in the water.

There are patches of aquatic canna, iris, and windmill grass on both sides of the river. "These plants are irrigated with tailwater from the nearby Nanshelang wastewater treatment plant. They beautify the environment while treating the sewage," said Zhong Jinju, a staff of the Songshan Lake Urban Construction Bureau.

"The place where the sea of flowers blooms is called the vertical flow constructed wetland. Generally, it is the efficient purification of sewage through plant absorption and microbial decomposition. After passing through the flowers, the sewage is discharged into the 'underwater forest' for further purification. The purified water is used for landscape replenishment, green land irrigation, road washing, industrial use, etc.," Zhong said. The deep-water purification system mainly uses the physical, chemical, microbial, and plant absorption effects of the artificial wetland and natural wetland to purify the sewage treatment plant's tailwater. Finally, it makes the surface sewage "inferior to Grade V" meet the standard of "Grade-IV" of sewage recycling.