Designated bathing water areas and bacteria measurements
In the UK there are currently only 19 bathing water sites on rivers. In Oxfordshire there are two designated river bathing waters; at Wolvercote in North Oxford and at Wallingford Bridge.
Designated bathing water status is granted to sites which have a high number of people swimming, paddling or bathing in the river.
Designated bathing water status means that the Environment Agency tests for two kinds of bacteria in the river water at the site during the bathing season, which runs from 15th May until 30th September. They should take samples at least 20 times during the bathing season.
The two different types of bacteria are Escherischia coli (EC) and Intestinal enterococci (IE). These bacteria indicate that there is faecal matter (poo!) in the water, which may come from human sewage but also from other animals (cows, horses, birds, dogs).
Higher levels of these bacteria pose a greater risk of illness to bathers, such as stomach upsets and skin and eye infections.
Each year, the Environment Agency gives each bathing water site a classification (poor, sufficient, good or excellent) based on the bacteria levels over the past 4 years. These are the levels required for each classification:
Inland Bathing Waters
| Excellent | EC: ≤500 cfu/100ml ; IE: ≤200 cfu/100ml (95th percentile) |
| Good | EC: ≤1000 cfu/100ml ; IE: ≤400 cfu/100ml (95th percentile) |
| Sufficient | EC: ≤900 cfu/100ml ; IE: ≤330 cfu/100ml (90th percentile) |
| Poor | means that the values are worse than the sufficient |
This looks quite complicated, but think of the 90th percentile as 90 out of 100 samples, and the 95th percentile as 95 out of 100 samples. Therefore, if the levels of E. Coli are over 900 cfu/100ml just 1 sample out of 10, then the site will be given a poor rating.
In this portal, we show the threshold between sufficient and poor levels for the two types of bacteria.
For more information, see the Environment Agency's information on bathing water quality.