After the "red sea" incident at Pantai Batu Hitam, Kuantan was again alarmed over another environmental mystery today when schools of dead fish were discovered in one of its rivers.

PAS Beserah state assemblyperson Andansura Rabu told Malaysiakini this was the first time such an incident had happened at Sungai Tunggak.

"There were thousands of dead fish for a four-kilometre stretch […] from the source of the river all the way to the sea," Andansura said.

He added that the cause of the phenomenon was currently unknown.

Andansura said the river flowed from an industrial area where chemical factories had been set up.

There also happens to be a bauxite stockpile in that area, he said.

"Whether this was caused by waste from the factories or by bauxite pollution or if someone poisoned the river, we don't know." the assemblyperson said.

He said the fisheries department has taken samples of the dead fish to determine their cause of death.

Andansura hopes the authorities will issue an order barring the public from using the river or fishing there as it could be potentially dangerous.

The dead fish mystery comes day after Kuantan's Pantai Baru Hitam turned red, allegedly due to bauxite pollution.

The Kuantan Port authority admits that there is run-off from bauxite stockpiles at the port, but denied that it was the source of the pollution.