August 2021: Dr. Lucy Dickinson gives an update on the Eynsham water testing program.


Since my initial report at the end of 2020, I have continued to monitor the phosphate and nitrate levels, adding some additional sites to the survey rota, including the Fishponds and two springs in private gardens. I have stopped recording ammonia and nitrite levels, as these were usually zero or very low (and the nitrite test is particularly time consuming), and instead focussed on widening the scope and trying to compare pollution levels at source (the springs) from those further downstream. We have also purchased a portable oximeter, and have dissolved oxygen levels for most sites for May, June, and July 2021.

Main findings

Levels continue to be unacceptably high at most sites. Nitrate levels are almost all above 1 ppm, with many being between 5 and 10 ppm:

 Nitrate levels August 2020 - August 2021


Nitrate levels in several locations showed a spike in March. This was shortly after the prolonged observation of tanker activity by Thames Water on the road near the Wharf Stream. Nitrate levels in the Fishponds were significantly lower than any other location, and zero for some months (May – July 2021). This pond is a large feature with water coming in from several sources, including the Abbey Barn Farms spring (Holywell), which has been significantly cleared and landscaped to allow the water to flow more freely since recording at this location started .


Phosphate levels August 2020-August 2021.


 Phosphate levels at all locations are also high- almost all above 0.1 ppm, with many sites much higher than this. There were huge spikes for the Lym Brook at Longmead in July 2021 (13.4 ppm), which also correlates with the results for the Lym Brook in South Leigh for that month beyond their sewage treatment station which showed a level of 250ppm, compared to around 10 times less than that further upstream (before the sewage plan). The fact that the raised levels persist within the water when it reaches the Thames indicates the impact. 

Oxygen levels from May – July 2021



Most of the levels are above 6 ppm which is apparently good for most kinds of pond animals (see South Leigh table:

0-2 ppm - not enough oxygen to support most animals

2-4 ppm - only a few kinds of fish and insects can survive Aquatic Earthworms, Leeches, Snails, True Flies

4-7 ppm - good for most kinds of pond animals Dragonflies and Damselflies, Craneflies, Alderflies, Crayfish, Clams and Mussels

7-11 ppm - very good for most stream fish Stoneflies, Mayflies, Water Beetles, Caddisflies

The levels in the Limb Brook and Fishponds appear to have dropped significantly in July, to a level of some concern (below 3 ppm).

Comparison of concentration for different countries: https://consult.environment- pressure-rbmp-2021.pdf

(UK is the highest for phosphates and second highest for nitrates)

Implications for planning (see upcoming seminar: office-to-residential-permitted-development-right/nitrate-neutrality-how-to-navigate-our-way-to- cleaner-waters?fbclid=IwAR1gnW5EO4aFz0gCcl-HXPwp85IaXdE0PIMtXZv0SFoFNaLWBq3oY-r5TmM

- It is a free online seminar about development and water issues)

-  Think about what work could be carried out in and around streams in Eynsham to improve the water health (e.g. the worrying levels in the stream in the Bartholomew playing fields, which is very clogged up and overgrown)

- Macroinvertebrates – examples of different types and what they tell us about the health of a stream. (


Thames 21 sites testing for e-coli and enterococci:



First set of results:

Help understanding the figures: data.html 

None of the areas samples reached bathing quality status for e-coli: oxfords-popular-swimming-spots-had-high-bacteria-levels-this-winter/

Real time alerts of sewage overflows by Twitter: (controversial - several volunteers have seen what looks like sewage when no overflows were reported).