Experts attributed the bloom to the worst snow in decades in the province. The abrupt rise in temperatures after the snow thawed killed a large amount of aquatic life which decayed and lead to excess nutrients, producing an unpleasant taste and odor.
The river's current lowered or stopped during the freezing weather in central China, which provided suitable environment for algae to grow and increase.
The Xinglong, Tianguan and Dongjing rivers are all distributaries of the Hanjiang River. Pollution was suspected as the cause when it was reported on Sunday that the water had turned a strange color.
Water companies were forced to cut supplies and use contingency sources. Residents had to rely on bottles of purified water and limited underground water.
Four teams were dispatched to inspect more than 30 factories along the rivers, but had identified no sources of pollution, according to the provincial environmental bureau.
"We would continue to inspect factories located in the source of water supplies across the province in case rivers were tainted by industrial pollution or chemical accidents," He said.
The bureau also planned to further promote water exchange by diverting water from Changhu Lake and Danjiangkou Reservoir during the low water period which was expected to last until late March.
Experts suggested paying more attention to water monitoring and protection after heavy snow and icy rain continuously hit southern and central China.
Last week, water pollution from homemade fertilizer affected the drinking water of 9,000 people in two towns in southwestern Yunnan province and killed 20 tons of farm fish.
Police arrested farmer Zhou Shunfu, who dumped 120 tonnes of waste residue containing phosphate on his fields, thinking that it could be used as fertilizer, and wiped out a neighbor’s fish farm.
(Xinhua News Agency February 28, 2008)