Each designated bathing water is classified every year as Excellent, Good, Sufficient or Poor, from the last four seasons of Environment Agency samples (Natural Resources Wales in Wales, SEPA in Scotland). It describes those samples, not the water on any one day.
Environment Agency samplers (Natural Resources Wales in Wales, SEPA in Scotland) test the water about weekly in the season for two bacteria from sewage and animal waste: E. coli and intestinal enterococci, counted per 100 ml. Lower is better. A "<" means below the lowest level the test can measure.
The change over the last three hours of readings. Rising means the level has gone up by more than 3 cm in that time, falling means it has gone down by more than 3 cm.
The band the gauge usually sits in. Above it, the river is high for this stretch and likely to be fast and cold. Below it, the river is low.
A storm overflow upstream is releasing untreated sewage mixed with rainwater into the river at this moment. The monitors report within about 15 minutes, so this is as live as the data gets.
A spill is one period during which a storm overflow released untreated sewage, mixed with rainwater, into the river. The feed reports when each one started and ended, and we count every spill from an upstream monitor.
We record every spill the feed reports from the day a monitor was first seen. The feed itself has no history, so the chart only goes back as far as our own records.
Every storm overflow monitor whose discharge flows past this spot: those higher up the same river, plus everything on tributaries that join above it. Distances follow the water, not a straight line.
The Environment Agency gauge (Natural Resources Wales in Wales, SEPA in Scotland) nearest this spot reads the water level every 15 minutes. Most gauges report the height above their own zero mark, so compare it with the typical range rather than other rivers.
Totals from the Environment Agency rain gauge (Natural Resources Wales in Wales, SEPA in Scotland) nearest this spot, summed from its 15 minute readings. Rain further up the catchment may differ, and heavy rain is what triggers overflows.