He agreed the tap water no longer smelled, but said the water crisis had caused a great deal of inconvenience to residents. He said almost everyone was complaining about the government's failure to control pollution.

Water specialists say officials from cities across the mainland should learn from the Tai Lake crisis and change their ingrained indifference to environmental protection.

At first, city officials insisted Wuxi's undrinkable tap water was a 'natural disaster'. They blamed the algal bloom on factors beyond their control - higher-than-normal temperatures, a lack of rain, wind conditions and the lowest water level in the lake in five decades.

The city sought to counter the problems by emergency measures. These included channelling water from the Yangtze River and local streams into the lake, inducing artificial rain, and, in a so-called 'bold move', pouring huge amounts of the oxidising agent potassium permanganate into the famed scenic location.

The situation was so grave the Communist Party mouthpiece People's Daily weighed in, slamming the city administration.

The Wuxi government again went on the offensive, unveiling a comprehensive environmental protection campaign. This included calling on businesses to reduce their output of waste and drafting plans to tighten waste-treatment standards. It also said more than 3 per cent of the city's budget would be spent on green causes.

But environmentalists are sceptical these remedies will work.

Tao Wenyi , an expert in water resources at Wuxi's Southern Yangtze University, said the chemical approach adopted by the city had eliminated the water's odour, but may also have left pollutant residue behind.

Jiang Wenlai , a water expert from the Chinese Academy of Agricultural Sciences, pointed out that the authorities had pledged to clean up the lake several times before.

'I hope they can realise those plans thoroughly and in a long-term way, instead of just showing their determination in the media,' Professor Jiang said.

Tai Lake straddles the border of Jiangsu and Zhejiang provinces. Its surrounding cities - Wuxi, Suzhou and Changzhou - are among the most affluent places in China, with economies that grew more than 15 per cent last year. Wuxi's gross domestic product was 336 billion yuan.

But the lake was also one of six major bodies of water identified by the government more than a decade ago as the nation's most seriously polluted.

The Guangming Daily quoted a State Environmental Protection Administration official as saying there had been 'worryingly slow progress' in reversing the pollution, and more than half of the projects designed to eliminate water contamination in the six areas were not effective.

Part of the central government's efforts to address the problem included an inspection campaign in the 1990s. Its goal was to shut down all big polluters around Tai Lake by 2000. More than 2,800 factories were pumping their effluent into the lake.

Professor Tao said the inspection campaign had little effect, and that pollution of the lake had increased in recent years, with residential and agricultural sources contributing to the problem.

'Even water let out from some wastewater-treatment facilities does not reach the standard level,' he said.

'And there are wastewater-treatment facilities at some factories laying idle that are only put into use during official inspections.'

He said no obvious progress to curb the pollution had been made, and much of the funding for pollution research and development projects had been misappropriated or used inefficiently.

Professor Jiang said water pollution was common across the mainland, and suggested there should be rules to punish officials in the event of an environmental crisis.

'Water quality in some rivers has deteriorated and the prognosis for all waterways is not optimistic,' he said. 'Officials should change their behaviour, which only focuses on GDP figures. Otherwise a similar crisis [to that in Wuxi] could happen elsewhere at any time.'

Professor Tao suggested a powerful pan-Tai Lake environmental protection authority could be established to veto development projects that would pollute the environment, and to co-ordinate with all related departments in Wuxi and other cities around the lake.