Tap water contamination, which had affected some 10,000 residents in a south China town earlier this week, was caused by freakish weather and sand dredging, which stirred up manganese from the riverbed into the water, environment experts said.

"The riverbed near the water plants' intake area might have a gravel layer with high levels of manganese," experts said in a report released Sunday by the environmental protection department in Guangdong Province, where the affected Da'an Town is located.

"Water levels at the Luohe River had fallen substantially before June 25 due to persistent drought, which exposed parts of the riverbed. Later, torrential rains triggered floods and washed manganese off the riverbed into the water," according to the report.

Additionally, sand dredging in nearby river areas also stirred manganese up into the water, it said.

Tests on Aug. 2 showed the amount of manganese in the water supply in Da'an Town was 12 times higher than the government safety level.

The manganese-tainted water came from Da'an Waterworks, one of the two tap water suppliers in the town. It provides water to more than 10,000 of the town's 50,000 residents.

It was the first manganese contamination case reported since the waterworks became operational in the 1980s.

Tests showed that water in other sections of the Luohe River had not been tainted.

Local government had warned the residents not to drink tap water before last Wednesday when supply was resumed by using temporary pipes connected to another local water plant.

According to the report, the manganese content at the intake was decreasing as the river's water levels were currently steady and the local government had suspended sand dredging in nearby areas.

"If the manganese content at the intake drops below the allowed level, it can be used as tap water again," said the report.

Environment experts also advised in the report that if the contamination risks cannot be eliminated, the plant should install facilities to demanganize water or find alternative water sources.

Health experts say manganese is a required nutrient, but high levels of the mineral can pose neurotoxic risks, causing mental and emotional disturbances and difficulty in moving.