The National Water Supply and Drainage Board is investigating the harm the oil leak near Diyagala could have caused to the water supply after the oil got mixed with the Mahaweli River.
A board official said that so far there was no immediate danger as the oil leak from a bowser which had toppled nearby had been contained.
However as some of the oil had leaked into the river a report had been sough over its impact to the public water supply as water from the river is drawn for public consumption.
The Disaster Management Center said that the fuel bowser had toppled near Diyagala along the Hatton-Colombo main road.
The driver of the truck had fallen asleep resulting in the truck going down a precipice early this morning. The driver has been arrested.
The Army, Police, Petroleum Corporation, Central Environment Authority and the water board were involved in containing the leak and assessing the impact it had caused.