For 73-year-old fisherman Ni Tingrong, who lives in a village on the northwestern shore of Taihu Lake, China's third largest freshwater lake, the idyllic scenes portrayed in the folk song "Beauty of Tai Hu" are confined to memory.

The lyrics go something like this: "Green reeds at the water's edge, rich in fish and shellfish at low tide, the lake water weaves through irrigation nets and the fragrance of fruit and rice wafts up from the lake."

But the modern-day reality is far from poetic.

"Just 20 years ago, I fished in the lake and the rivers nearby almost everyday," said Ni, who began working as a fisherman at the age of 14. "But pollution has only left us blue-green algae and the odor of dirty water, the fish stocks are drying up."

Taihu's nightmare

Covering an area of 2,400 square kilometers in east China, Taihu Lake is a major source of drinking water for people living in Shanghai and Jiangsu and Zhejiang provinces. Historically a rich and fertile area, the lake region has become one of the most populous and prosperous regions in the country with 33.5 million people living in the surrounding area.

However, the lake has come under increasing environmental strain for years as untreated sewage from towns and villages, as well as the region's booming chemical and light manufacturing industries, have choked its water with pollutants.

The fine line between rapid economic growth and continuous ecological degeneration was crossed in May when a large bloom of blue-green algae was found to have swamped the lake. The combination of the low water level and the accumulation of waste and untreated sewage had triggered the algae bloom, turning the water putrid and cutting the water supply to more than two million residents.

Workers collected thousands of tons of algae from the lake and residents raced for bottled water.

It was not the first time Ni had seen the lake water clogged up with waste in his hometown of Zhoutie, outside Yixing City, in Jiangsu Province, home to more than 100 chemical plants.

"Actually, all the families in our village have been using water from the nearby well, instead of that from Taihu Lake, as drinking water since 1998, because the lake water had a weird smell of chemicals," said Ni.

The old man said Zhoutie Town saw its first chemical plant 15 years ago and so many others followed in the space of one decade that the town soon won a reputation as the "hometown of chemical plants".

The booming chemical industry has inspired the economic growth of Zhoutie Town, but the industrial waste has also brought environmental disaster to its residents with urban sewage and chemical fertilizers from agriculture.

"Black water flows directly into the lake. Soon fish in the rivers nearby died and we had to fish in the large lake," said Ni.

"There is still fish in the lake, but the quantity is reducing because the lake is being polluted too."

Zhoutie Town is no exception to the Taihu Lake region. Around 20,000 chemical plants that cluster in the Taihu valley have had a drastic effect on the water quality of the lake.

Experts say that the lake's environmental problems include accelerated eutrophication, or aging, caused by nitrogen and phosphorus enrichment. These materials cause an overgrowth of algae and further deterioration, including oxygen depletion.

Investigations from the State Environmental Protection Administration (SEPA) show that the content of nitrogen in the lake in 2006 was three times the amount in 1996, while the content of phosphate pollutants had increased 1.5 times in the 1996-2006 period.

To mitigate the lake's environment pressure, all towns around Taihu Lake have been ordered to establish sewage treatment plants and are forbidden from discharging untreated sewage into the lake and rivers in the Taihu valley.

Existing plants must also install nitrogen and phosphorus removal facilities and those that fail to meet the raised water emission standards risk suspension. They will be shut down permanently if they still fail to meet the standards by the end of next June.

In addition, more than 1,000 small-sized chemical plants that are scattered around rivers and lakes have been closed since June in the cities of Wuxi, Suzhou and Changzhou in Jiangsu.

In Zhoutie alone, 93 chemical plants were closed in the past three months and more than 40 others are left, said Wu Xijun, Party chief of the town's government.

"After the algae incident, voices to reform the chemical plants are coming from everywhere and we have felt more pressure than ever, so we know we have no other choice but to close the plants," said Wu.

"I hope the policies will be faithfully implemented," said Ni, "or what an irony it will be, if we have no water to drink though the lake is right before our eyes."