THE River Usk has the highest incidence of phosphate pollution among Wales’ nine river Special Areas of Conservation, while the Wye is ranked equal second worst.

A report by Natural Resources Wales (NRW) said sampling on several stretches of the Usk saw an 88 per cent phosphate failure rate, while the Wye recorded a 67 per cent failure rate, which some environmentalists have linked to a growth in poultry farming in Powys, following green algal growth in recent summers.

Fertiliser run-off from agriculture, human and animal waste and industrial effluent are among causes of high phosphate levels. The other seven SACs alongside the Usk and Wye in Wales are the Cleddau, Eden, Gwyrfai, Teifi, Tywi, Glaslyn and Dee. These rivers support some of Wales’ most special wildlife such as Atlantic salmon, freshwater pearl mussel, white-clawed crayfish and floating water-plantain, but high phosphate levels put them all at risk.

New targets set by the Joint Nature Conservation Committee (JNCC) recommended the adoption of tighter targets in considering new evidence about the environmental impacts of phosphate.

In addition, the predicted warmer and drier weather resulting from climate change could reduce river flows during the summer, and so increase concentrations. An NRW spokesperson said: “Following the new measures, this evidence review shows that overall, phosphorus breaches are widespread within Welsh SAC rivers with over 60 per cent of waterbodies failing against the challenging targets set.

“The river with the highest level of phosphate failures was the Usk with 88 per cent of its water bodies failing their target.

“Previously published data about the Wye, as well as new data on the Cleddau shows that over 60 per cent of river sections failed their targets.”

Ruth Jenkins, NRW’s Head of Natural Resource Management, said: “Phosphate can cause significant ecological damage to rivers and can lead to the process of eutrophication (algal growth) in rivers, a highly problematic issue.

“Conservation standards were tightened as a means of safeguarding the river environment and countering the impacts of climate change.

“The new targets set for phosphate levels in our rivers are challenging – but rightly so.

“By sharing this information, we can all better understand how nutrient levels such as phosphate affect our rivers and we can work together with policy makers, businesses, land managers and residents to protect the river and the natural resources it provides for people.

“We all have a part to play to make sure that Wales’ rivers are healthy for future generations. Simple changes we can each make in our everyday lives can help make a positive contribution to the reduction of phosphate levels and other forms of pollution affecting our rivers.”

The 78-mile long Usk rises in the westernmost part of the Brecon Beacons and flows through Brecon, Crickhowell, Abergavenny, Usk and into the sea at Newport, while the 155-mile Wye rises in mid-Wales and flows through Rhayader, Builth Wells, Hay-on-Wye, Hereford, Ross-on-Wye, Symonds Yat, Monmouth and Tintern, before meeting the Severn estuary in Chepstow.

While phosphate is naturally occurring, and is released slowly, at low levels, from natural sources, such as natural bankside erosion, it can also enter rivers from land management practices, sewerage and foul water that can contain detergents and food waste.

The report suggests a number of areas where work can be focussed, and includes working with planning authorities across Wales to help them understand what the findings of the investigation could mean for their planning processes.

Last summer, a row erupted over the impact on the river of the higher levels of phosphate, after the Wye was seen to turn green. Environmental groups such as the Wye and Usk foundation blamed manure from a growth in poultry farms upriver.

But farmers hit back by saying there were a range of issues to consider as well as physical modifications that alter flows and barriers impeding fish migration.