The transparency of the lake reached 60.07 centimetres on average in 2004.
That means objects to a depth of about 60 centimetres are visible to the naked eye, according to a report from the West Lake Waters' Administration Division in Hangzhou, capital of East China's Zhejiang Province.
"The West Lake has witnessed the best water quality ever recorded in history and the transparency continues to rise," said Wu Zhiying, vice-director of the division.
Compared with 2003 and 2002, the average clearness of the water increased by 10.65 centimetres and 16.41 centimetres respectively, according to the report.
The West Lake, covering 6.5 square kilometres, is the most important scenic spot in Hangzhou. Iat has been famous for thousands of years for its intoxicating beauty. It was originally a shallow sea inlet before it became a lake due to the laying down of silt.
The increased transparency of this water wonderland is down to the success of a West Lake protection project, launched in 2003 by the local government to improve water quality, Wu said.
About 400,000 cubic metres of recycled water is drawn from the Qiantang River into the lake each day, meaning the water is completely changed each month.
"This provides a total volume of 120 million cubic metres of fresh water into the lake every year and the West Lake has become a flowing lake now," said Wu, adding that the water was changed yearly in the past.
What is more, the self-purification ability of the lake has been greatly improved thanks to the "westward movement."
That has reclaimed wetlands in the western part and enlarged the area of the lake from 5.6 square kilometres to 6.5 square kilometres, according to Wu.
The average depth of the lake has increased from 1.65 metres to 2.27 metres with a volume of 14 million cubic metres, 40 per cent higher than before.
Efforts have also been made on a waste discharge system to solve the problem of waste water being dumped in the lake by farmers living nearby, said Wu.
To maintain a balanced ecosystem, more than 1 million plants - about 66 types in all - have been planted around the lake, making it a venue for birds such as wild ducks and cormorants.
However, the hardest nut to crack is how to fully rehabilitate the ecosystem of the West Lake, Wu says.
"There is still a long way for us to go to strike a balance between human and nature," Wu added.
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