AN investigation into a pollution spill which caused the death of some 50,000 fish in a River Wye tributary has been labelled "feeble" and "an utter disgrace" after the probe was ended without any prosecution.

Natural Resources Wales announced there was "no realistic prospect of conviction" over the incident nearly a year and a half ago on the River Llynfi near Glasbury.

Powys councillor William Powell labelled the failed investigation the body’s "darkest hour", telling our sister paper The Brecon & Radnor Times it was clear the body was "woefully under-resourced" to deal with the incident in a "timely manner".

But the NRW said its investigation team had worked "tirelessly to investigate and seek to gather evidence" to bring those responsible to justice.

Ann Weedy, NRW operations manager for NRW in mid Wales, said: "Our officers have been appalled by the damage caused to the River Llynfi by this incident and are very disappointed that we have not been able to bring those responsible to justice.

"The River Llynfi is a Site of Special Scientific Interest in a Special Area of Conservation. The fact that such a significant number of aquatic animals died in the incident shows just how rich the wildlife was in this small tributary river.

"Thankfully, assessments we carried out earlier this year are showing promising signs of recovery in the river.

"We have exhausted every lead and done everything we can to be able to prove what happened, but with the deepest regret, this investigation has now ended.

"We will consider reopening the investigation if compelling new evidence comes to light. If anyone has such evidence, we urge them to contact us.

"We were determined to hold the person or people responsible for the pollution to account. We took our time and worked methodically to make sure we left no stone unturned."

But Cllr Powell said: "It’s the darkest hour in the history of Natural Resources Wales since it came into being on April 1, 2013.

"Residents, lovers of the Llynfi and the Wye and all fair-minded people have waited patiently for justice, only for it to end with a feeble press release."

The Lib Dem councillor added: "It is essential lessons are learnt from this sorry episode. One key point is around resources and it is clear the NRW was woefully under-resourced to deal with the incident in a timely manner.

"The attention of the whole country has been drawn to the Wye and its tributaries by this environmental disaster. It is imperative that it is not allowed to happen again."

Green Powys councillor Emily Durrant labelled the failed probe an "utter disgrace" and called for an independent review into NRW’s actions.

"NRW is not fit for purpose if it can’t even enforce a major point source pollution event like this one. Devastated doesn’t come close," she said.

Witnesses described seeing hundreds of dead fish and crayfish in the Llynfi between Glasbury and Talgarth on August 1, 2020.

Dead fish, pictured above, included brown trout and eels, while crayfish were seen "crawling up the bank to escape the water".