Blue-green algae-which has threatened Dianchi Lake, the biggest lake in Southwest China's Yunnan Province, for three decades-will soon be out of control again.

The provincial government has spent more than 3 billion yuan ( US$ 361 million) during the past decade trying to bring the algae under control. Blue-green algae, a kind of water plant, grows easily in polluted water with a high concentration of nitrogen and phosphorus and with temperatures around 18 degree centigrade. Too much blue-green algae will remove oxygen from the water killing fish and other aquatic life, and can turn Dianchi into a " dead" lake. Blue-green algae had been threatening Dianchi Lake since 1970s. In 1999, blue-green algae covered 20 square kilometres of the lake, one-fifteenth of the lake's total area. Since 1983, the provincial government has tried to curb the growth of blue-green algae. Four sewage treatment plants were built near the lake. They are able to treat of a total of 365,000 tons of wasterwater each day. In 1999, a government-led campaign spurred 249 of the 253 factories along the lake to stop dumping their industrial sewage into the lake. The government also spent 250 million yuan ( US $ 30 million) to dredge 4.2 million cubic metres of mud. The network to collect sewage is incomplete, and more than 80 per cent of domestic sewage with fertilizers and pesticides still flow into the lake through 16 rivers.

Located in Lu'nan Yi nationality autonomous country ( area 1,777 square kilometres, population 220,000), in southeast Yunan province, the Stone Forest is described by people as having " the most fantastic scenery in China."

Formed 270 to 300 million years ago, the Stone Forest consists of 352 square kilometres ( 352,000 hectares or 869,792 acres) of typical karst that has been developed) of which are the most frequently visited for their concentration of stone formations. It is 120 kilometres from Kunming, capital of Yunnan Province.

From a distance, it indeed resembles a dense forest, but as the tourist draws closer he will find the" tress" are all slender stone pinnacles. Geologists say that the Stone Forest is a special type of limestone formation know as karst ( a region made up of porous limestone containing deep fissures and sinkholes and characterized by underground caves and streams). Some 200 million years ago this area was submerged under a thick layer of limestone at the bottom of the sea. Latter, the movement of the earth's crust caused the sea bottom to thrust upward and became land. Owing to solvent action, long deep cracks developed in the limestone, and rainwater running through the cracks gradually eroded the stone into the present shapes.