Water Quality data

This page shows the results of water quality monitoring that we’ve been undertaking during 2021, aiming to understand the sources of poor water quality on the River Cam around Cambridge.

Chalk streams should be crystal clear and unpolluted. The Cam should be too, but isn’t. To explore this, we’re monitoring water clarity by taking photos, and having samples analysed for ecoli bacteria (which shows if there’s poo in the water), Phosphates and Nitrates.

In the map above, ecoli readings on 14 June are shown in 4 bands, ranging from the worst, which are shown with deep purple markers, to the best, which is shown in yellow. Click on the marker to see the reading in units of ecoli/ 100ml of river water, or on the photo ( taken on July 7th) to see a larger image.

For more detailed results, and to access the source map so you can change which layers are displayed, click here

The official standards for bathing water are complicated, and often based on multiple readings over a period of time. For simplicity, we’re setting an aspirational target for the Cam of no more than 100 ecoli/100ml. This is based on the EU’s guidelines for high quality bathing water that are “to be achieved where possible” and the more stringent American standards. Note that drinking water should have no ecoli at all. ie 0 ecoli/100ml, and all of our readings show more than this.

We are sharing the results so that those interested can join us in helping to improve the quality of water in the Cam. Although we expect that swimmers and other water users will find the results of great interest, please note that this should NOT be taken as guidance as to where or when its safe to swim.

  • We are amateur volunteers, NOT experts, and although we’re using a professional lab to analyse the results, we are using a simplified procedure because otherwise it’s too expensive for us. Definitive analysis results are available from the Environment Agency, but unfortunately only after a year’s delay.
  • We know that changes in weather and rainfall will influence the results, and are trying to understand this process. This means that the conditions when the test was taken, may be very different to the situation today.

Our general advice is to

  • Use your own judgement about when and where its safe for you to swim.
  • NEVER drink water from the Cam (always keep your mouth shut when swimming)
  • Shower as soon as possible after leaving the water, particularly if you’ve got muddy.
  • Don’t swim just downstream of Haslingfield Sewage Works

We hope to be able to develop more detailed advice after we’ve done more work.

Do join us. We also very much welcome contributions to the costs of the lab analysis, which costs us just under £1000 per set of readings.