One source of water pollution is from mud and sediment washed in by rainwater from building sites. The movement of traffic, digging or moving of soil and general disturbance all have the potential to wash sediment into rivers and streams.
Together with polluting the water this sediment can settle over gravels and smother them, destroying spawning habitat for fish. The sediment might also clog or block the gills of fish and breathing apertures of invertebrates.
Natural Resources Wales is responsible for ensuring water quality is protected. Along with the National Park Authority, NRW may request certain measures to be included in the planning permission, or may recommend that permission is refused.
View NRW’s advice on water quality issues here.