What Excellent, Good, Sufficient and Poor actually mean

Ireland, England, Wales, Scotland and Northern Ireland all classify bathing waters under the same rules, which come from the EU Bathing Water Directive (2006/7/EC). The UK kept the standard after leaving the EU, so a beach in Cornwall and a beach in Kerry are graded by an identical test.

That shared standard is the reason a site like this one can cover several countries at once. It is also why a classification from one agency can be compared with a classification from another — something you genuinely cannot do with most environmental data.

The test measures two things, and only two: Escherichia coli and intestinal enterococci. Both are indicator bacteria. Nobody particularly cares about them in themselves — they are measured because they are reliable markers of faecal contamination from sewage and agricultural runoff, which is what actually makes swimmers ill.

Counts are given per 100 millilitres of water. Coastal and transitional waters are held to tighter limits than inland lakes and rivers, because seawater is a harsher environment for these bacteria and the same count therefore implies more contamination.

• Coastal and transitional — Excellent: 250 E. coli and 100 intestinal enterococci, at the 95th percentile.
• Coastal and transitional — Good: 500 E. coli and 200 intestinal enterococci, at the 95th percentile.
• Coastal and transitional — Sufficient: 500 E. coli and 185 intestinal enterococci, at the 90th percentile.
• Inland — Excellent: 500 E. coli and 200 intestinal enterococci, at the 95th percentile.
• Inland — Good: 1,000 E. coli and 400 intestinal enterococci, at the 95th percentile.
• Inland — Sufficient: 900 E. coli and 330 intestinal enterococci, at the 90th percentile.

Poor is simply what a water is called when it fails to reach Sufficient. It is not a separate measurement.

The sample charts on this site draw a dashed reference line at 500 E. coli per 100 ml for coastal waters, which is the Good threshold. It is context for reading the chart, not a pass mark for any single sample — see the next section for why that distinction matters.

This is the part that surprises people, and it is the single most useful thing to understand about these numbers. A classification is not an average and it is not a worst case. It is a percentile calculated across four consecutive bathing seasons — typically around sixteen samples a season, so around sixty-five readings in total.

A 95th-percentile limit of 250 E. coli means, roughly, that the statistical model fitted to those sixty-odd readings must put 95% of them below 250. One high reading among sixty-five moves that model very little. Two seasons of consistently high readings move it a great deal.

So a beach rated Excellent can absolutely have had a sample come back at 1,000 last July. That is normal, it is visible in the sample table on the spot page, and it does not mean the rating is wrong or out of date. It means one sample was taken shortly after heavy rain, or a gull colony was having a good week.

The reverse is the more important point. Because the rating is a four-year statistic, it tells you very little about today. A beach rated Excellent can be under a sewage discharge this afternoon. That is what the live alerts and short-term pollution forecasts are for, and why this site shows a current status separately from the annual rating.

A Poor classification has consequences beyond the label. The agency must put up signage advising against bathing for the following season, must tell the public why, and must set out what is being done about it. In England this appears as the advice-against-bathing list, which is what turns a spot red on this site.

If a water is rated Poor for five consecutive years, a permanent advice against bathing follows and the site can be de-designated — removed from the monitoring programme altogether. That is worth knowing, because de-designation makes a beach disappear from the data rather than improve. A beach with no classification is not the same as a beach with a good one.

You can see every currently Poor-rated bathing water in the UK on the Poor water quality list, and everything currently under an active warning on the UK warnings page or the Ireland warnings page.

The two things it measures are faecal indicator bacteria. It is silent on everything else, and the gaps are worth naming plainly.

• Chemical pollution, metals, pesticides and microplastics are not part of this test.
• Algal blooms are assessed separately and can close a beach that is rated Excellent.
• Litter, oil and visible pollution are not graded.
• Nothing about tides, rip currents, swell, water temperature or cold water shock — which are what most often cause harm. See the cold water swimming guide.
• Sampling only happens during the bathing season, which runs roughly June to mid-September in Ireland and mid-May to end of September in the UK. Winter swimmers are swimming in unmonitored water.

That last point is underappreciated. The year-round swimming community — the people most likely to be in the water in February — are the people for whom the least data exists.

Three habits make these ratings much more informative than the single word suggests.

1. Look at the four-year trend, not just this year. A water that has been Excellent four years running is a different proposition from one that has just climbed out of Poor, and both display the same word. Every spot page on this site shows the run.
2. Check whether there is a live warning today, separately from the rating. The annual classification and the current status answer different questions.
3. Check when it last rained. Short-term pollution is overwhelmingly rain-driven — see swimming after heavy rain.