Carmarthenshire diesel spill: Thieves cause river pollution
Thieves have caused a diesel spill while trying to steal 70,000 litres of fuel from a depot.
They laid a pipe from Oil4Wales' depot in Nantycaws, Carmarthenshire, to a layby on the A48 late on Friday night.
But the pipe leaked in the field they laid it through, resulting in the spill into the Nant Pibwr early on Saturday.
Dyfed-Powys Police is investigating and Natural Resources Wales (NRW) said diversion ditches and a boom were in place to try and contain the spill.
It is not yet known how much fuel has leaked into the river.
The same tributary of the River Tywi was hit by a kerosene spill in 2016.
"Distressed" fish have since been seen in the river as officials examine the extent of the impact, NRW said.
"We were made aware of oil pollution in the Nant Pibwr on Saturday and sent officers to investigate the incident," said manager Andrea Winterton.
"Officers and specialist contractors are in attendance and are implementing a mitigation plan that includes downstream boom placement and interceptor ditches."
Police said the thieves struck between 22:30 GMT on Friday and 00:30 on Saturday.