The local environmental protection bureau in Central China's Henan province is investigating why water in a river became red.

Located in the newly developed downtown area of Zhengzhou, capital of Henan province, the Qili River was red on the morning of July 10 after a heavy rain fell on the city for several days.

Some dead fish could still be found floating on the surface of the river on the morning of July 11, along with trash including plastic bags and bottles.

An official from the publicity department of the Zhengzhou environmental protection bureau told China Daily on July 11 that the river was polluted but the cause is still being investigated.

"The river runs through the downtown region and lots of residents walk around it every day," the official said on condition of anonymity. "The pollution made the places around it smell terrible, and we will make sure that it becomes clean again as soon as possible.

A local female resident surnamed Liu told the Dahe Daily that the water in the river was clean on July 9, and she was confused why it became red overnight.

A worker cleaning the river said that the water made him feel itchy after he stepped into it.

The river is likely polluted by factories upstream, as they expel a lot of polluted water into the river when it rains, according to an official from the local water authority.