This chart is compiled from weekly analyses which are averaged to produce quarterly results for each of the sampling sites.

Measurement units: Colony forming units per 1millilitre of sampled water (Cfu/ml).

The UK has adopted international bathing water standards. A commonly used benchmark for E.coli is 500 Cfu/100ml (5 Cfu/ml), below which the water quality is classified as Excellent, and is shown as the horizontal line on the chart. Readings above 900 Cfu (9 Cfu/ml) indicate the water body is unsuitable for bathing.