Tai (great)-hu (lake) is the third largest freshwater lake of China, below in size Lakes Poyang and Dongting, situated about 100 km from the east coast of the Chang Jiang delta in central China. The whole lake is under the administration of Jiangsu Province, though its southern coast belongs to the neighboring province, Zhejang. It is located in the densely populated fertile plain of the delta known for its complicated network of small lakes, ponds, streams and man-made canals, including the Grand Canal built in the 7th century to connect Beijing with Hangzhou in Zhejang.

The inflowing water comes mainly from mountains to the west and southwest of the lake, while the draining rivers start mostly from the east coast of the lake. Several rivers and channels connect the lake with Chang Jiang, but the water flux is controlled by dams to maintain the lake water level within a range of fluctuation of 2-3 meters.

The lake is famous for its abundant production of fishes and crabs, and the aquaculture farms on the coast that apply skillful techniques. In addition to supporting heavy boat traffic, Tai-hu provides some of the best known water- side scenery in China for domestic and foreign sightseeing visitors.

Tai-hu and its effluent rivers are important sources of water for the inhabitants and rapidly increasing industrial factories in Shanghai, Wuxi, Suzhou and other neighboring cities, so that the pollution of the lake is a serious social concern. The pollutants originate mainly from home sewage of the vast number of inhabitants, agricultural pesticides applied over fields in the drainage basin, and the industrial sewage of more than 700 factories and mines. The Film Studio, Tanshan Ore Dressing Plant, West-hill Mines and the Wuxi No.3 Instrument and Metal Plant discharge 2,750 tons per day of waste water directly into the lake. Phenol, mercury, chromium etc. are widely detected over the lake, but at fairly low concentrations. The lake water is also highly eutrophic, with frequent blooms of blue-green algae even in late autumn (1, 2).