A second potentially dangerous algae bloom has been reported in an eastern Chinese lake. Joseph Popiolkowski reports from Hong Kong that the big worry is over the effect the algae will have on the safety of drinking water.

Last week, an algae bloom in eastern China's Lake Taihu spurred authorities to cut off drinking water to the city of Wuxi, forcing residents to drink and wash using bottled water.

China's state-run media reported that environmental authorities are monitoring another algae bloom in Lake Chao, China's fifth largest freshwater source.

Algae are simple aquatic organisms. When high levels of nitrogen, or other nutrients, are introduced into the water, algae grow rapidly, killing and feeding off other life forms. Some algae blooms can produce biotoxins harmful to humans that freely pass through water treatment systems.

One expert says pollution from industrial run-off is the major contributor to the algae blooms.

Wen Bo, China Program Director for the U.S.-based activist group Pacific Environment, says algae blooms are not uncommon in China's increasingly polluted lakes.

"This one has just become dramatic because it affects a large city - Wuxi city - and it has contaminated their drinking water," Wen explained.

An environmental activist in Wuxi, Wu Lihong, had warned officials for years about worsening pollution in Lake Taihu but was arrested in April on what friends and family say are trumped up extortion charges.

Wen says the activist pushed too far into investigating the links between local officials and companies that pollute China's lakes.

"He didn't conduct any serious crime. And that's so dramatic that just a few weeks after his arrest there was a serious crisis with drinking water in Wuxi city," Wen noted.

China's state-run media say the recently reported bloom in Lake Chao is not a threat to drinking water in nearby towns and has been diluted by rainwater.

Chinese media also say the water in Lake Taihu is again drinkable after environmental officials seeded rain clouds and flooded the lake with water from the Yangtze River.