Natural Resources Wales has said phosphate levels in the River Wye are in decline as it responded to a group which said chicken farms were to blame for the water turning green.

Earlier this week, the Wye and Usk Foundation released a statement claiming that algal blooms which had discoloured the river – potentially harming plant life beneath the surface – were in part because of intensive poultry farming's growth in Powys.

That drew an angry response from local farming groups, who insisted that a wider range of issues was at play – and now Wales's environment agency has provided its own perspective on the issue.

Ann Weedy, Mid Wales operations manager for Natural Resources Wales said: “Algal blooms can develop in rivers when a number of factors occur at the same time. These can include low river levels, periods of sunny weather and warm water temperatures, and when there are nutrients present in the river.

“The recent algal blooms in the River Wye come at a time where river levels have been close to the lowest recorded levels and following the sunniest May on record in the UK. These factors combine to warm water temperatures.

“Long term phosphate levels in the Wye catchment have been declining which is good for the health of the river. This decline in phosphate levels is due to many factors such as the Dŵr Cymru Welsh Water investment in the Llandrindod Wells Sewage Works.

“As part of our pollution reduction activity, we work closely with the agricultural community to minimise nutrient run-off into rivers. We regulate any poultry units which have over 40,000 birds and issue permits which contain conditions to protect the environment. Large poultry units are required to dispose of their manure in accordance with a manure management plan.

“We have also been undertaking a series of proactive visits to a number of poultry units along the River Ithon which do not need an environmental permit under current regulations. We offered free nutrient management planning and soil testing as part of our visits. None of these visits identified serious issues.

“Members of the public can report cases of pollution to NRW by calling our incident number 0300 065 3000, which is available 24 hours a day.”