A new study has found that farmers in Pembrokeshire could help clean up the heavily polluted Eastern and Western Cleddau rivers while also cutting their costs, by better managing the phosphorus in fertiliser and animal feed. The rivers, which are protected special areas of conservation, have been rated Wales' poorest performing waterways, with excess nutrients feeding algal blooms that starve fish and other wildlife of oxygen. The pollution has become severe enough to trigger restrictions on new house building locally, and researchers now say agriculture is the primary driver of the problem.

Researchers from Lancaster University, funded by the Welsh government, found local dairy farms were importing far more fertiliser and processed feed than necessary, leaving a surplus of about 360 tonnes of phosphorus in the land each year, roughly the weight of 26 double-decker buses. They concluded farms already produce enough phosphorus in manure and slurry to meet crop needs, meaning better spreading of these materials could cut reliance on costly artificial fertiliser and save Pembrokeshire's farmers an estimated £1.08m a year. Hundreds of dairy farms, in an area producing up to a quarter of Wales' milk, are now calculating their "nutrient footprint" as part of what is thought to be one of the largest projects of its kind in the world.