Llanishen Reservoir was rated Excellent for 2025 — the highest of the four grades in the Bathing Water Regulations. That grade comes from bacterial samples taken over several seasons, so it describes the beach's record rather than the water on any given day.
Natural Resources Wales issues a daily pollution risk forecast during the bathing season, and Dŵr Cymru publishes live storm overflow status.
The regulator records this as a bathing water whose quality can be affected by heavy rain, which is why rainfall in the last 24 hours is shown above.