3,500 litres of oil pollutes River Usk at Crickhowell
About 3,500 litres of oil has leaked into a river in Powys.
Dead fish have been spotted on the river in Crickhowell where an 850m stretch has been affected, said Natural Resources Wales (NRW).
Officers have identified the source in the Cwm Beth tributary, but the oil has worked its way downstream to the main River Usk.
It has left an oily sheen on top of the water and a strong odour.
Rhys Hughes, from NRW, said: "Our officers have already spotted a few dead fish in the river, but we're expecting to see more as the pollution moves through the system.
"Our team have put booms in place in the Cwm Beth to soak up as much of the pollution as possible.
"Our fisheries specialists are also currently conducting a full assessment of the river to help us determine the impact on the wildlife in the river."