NANJING -- In the first half of this year, the water quality of Taihu Lake, the country's third largest freshwater lake, in East China's Jiangsu province, reached the best level in the past 10 years, said the provincial department of ecology and environment.

From January to June, the average water quality of Taihu Lake was recorded as Class IV in the country's five-tier water quality system.

Taihu Lake is also an important source of drinking water in the Yangtze River Delta. Over the past 10 years, the water quality of the lake has been significantly improved, with the concentration of ammonia nitrogen down by 63.6 percent, total phosphorus down by 1.6 percent, total nitrogen down by 42.2 percent, and the density of blue-green algae reduced by 8.4 percent.

The water quality of 15 major rivers entering the lake has reached or exceeded Class III, and the number of aquatic species in the lake has increased to 342, according to the department.