70,000 fish deaths investigated in Olway Brook, Llansoy
An investigation is continuing after more than 70,000 fish were found dead in a Monmouthshire stream.
Natural Resources Wales (NRW) said the water quality at Olway Brook, near Llansoy, was improving after trout, eel and lamprey were found dead last month.
The environmental body is investigating whether the fish were poisoned and is considering its "enforcement options".
It said the impact on the fish population was significant and the situation was being monitored.
A spokesman for NRW said: "Monitoring will continue throughout the week and the impact on the fish and invertebrate population will be assessed.
"The impact on fish population in the stretch affected has been significant. We will consider our enforcement options when the investigation into this incident is completed."