Southwest China's Guizhou province has strengthened pollution control around an upper tributary of the Yangtze River, with 82 enterprises being punished, the provincial environmental protection department said Tuesday.

The Wujiang River is the longest tributary on the southern bank of the upper reaches of Yangtze, China's longest river. As a major river in Guizhou, the Wujiang River basin covers one third of the province's land area.

Nine enterprises in the basin were closed after no environmental impact assessment procedures or no environmental protection facilities were found; seven companies were transferred to judicial organs for unlicensed sewage disposal and refusal to improve; and 21 enterprises were suspended for their lack of environmental protection facilities or using inefficient environmental protection facilities, the department said.

Another 45 enterprises are under administrative penalty for illegal environmental activities, it said.

The Wujiang River basin has long been plagued by problems such as industrial pollution and urban sewage pollution as the region saw rapid economic development and urbanization but lacked advanced anti-pollution facilities.