Powerful insecticides such as diazinon (used in sheep dipping) and cypermethrin which is used in some forestry operations have been entering rivers. Even in very small doses, these chemicals can do significant damage to aquatic insects and to fish.
Also with soil comes more toxic chemicals such as pesticides and herbicides. Some of these are used in agriculture to protect crops but land in Wales is also used for the disposal of chemicals and sludge from the sewage treatment process.
The recent 2025 Interim WFD Classification by Natural Resources Wales now shows increasing concerns from the insecticides diazinon (used in sheep dip) and cypermethrin (used in forestry) in their river sampling.