Phosphate is an essential nutrient for plant growth. On land it helps to grow crops but excessive amounts in water leads to algal blooms. These blooms not only turn the rivers green but also lead to lowered oxygen levels at dawn.

Algal blooms also shade out and eliminate the water crowfoot (Rannuculus sp.), which provides important fish and invertebrate habitat.

The photo on the right shows the normally clear upper Wye during a summer algal bloom.

See here for what we are doing to reduce the amount of phosphate entering the rivers.