2nd February 2026 River Deben Environment Monitoring Results

This month’s sampling on Monday 2nd February followed several days of rain the week before, notably with around 25 mm on Tuesday 27th and a further 10 mm on Friday 30th (Woodbridge rainfall data). River levels were still high on Monday and fields were still flooded in places; several of our sampling points at Anglian Water outfalls were underwater, which has affected the results below.

1. E.coli

Due in large part to the higher river flows and levels, E.coli numbers are dramatically down in several places, most notably at and below the Anglian Water and other outfalls. For example the STW sample point at Henley, previously around 200 to 500 colonies per 1ml fell to 3 colonies per 1ml. 

A new sample point in Run Meadow on a small stream which runs into the River Fynn at Martlesham showed 97 colonies per 1ml, similar to samples taken in mid-January before the heavy rain. We are planning to trace this stream as there are private outfalls and industrial activities further up towards Kesgrave. 

In the tidal zone, there was no such impact with Martlesham Creek and the Kyson Point to Wilford Bridge section around or only somewhat above trend. This slightly higher background level may be accounted for by the 78 hour CSO spill recorded at the Deben Road operation in the previous week.

At Debenham, E.coli levels were similarly well down with only 3 of the 16 sampling points showing any cause for concern at all. Taken with the section below towards Easton, this whole area showed low levels of bacterial pollution.

2. Phosphate

Here again, high river levels and faster flows had a dramatic impact on phosphate numbers. None of the usual “red flag” sample points close to or at STW’s in the non-tidal section, showed significant phosphate levels. For example, the Rendlesham outfall recorded only 0.82 mg/litre as against the 5 to 10 mg/litre trend; this outfall was underwater when the sample was taken.

In the tidal section, we recorded a massive phosphate spike of 3.33 mg/ litre at Kyson Point, close to the Martlesham Creek STW. This reading is at least 25 times any previous number recorded here. We took a further sample on Wednesday 4th February which showed a reading of 2.41 mg/ litre. We are concerned that there may have been a spillage from an industrial or other source as the usual down stream impact from Martlesham STW does not account for these levels. The issue has been reported to the Environment Agency for investigation.

At Debenham, phosphate numbers were down on the usual levels, with only a couple of points above the 0.1 mg/litre “healthy river” target. This is almost certainly due to the high flow.

3. Nitrate

The chart below shows the dramatic impact of higher flows in that with STW outfalls mainly underwater, none of the usual spikes at these points are evident. However, nitrate levels in the river are almost all at or above the danger 50 ppm level in spite of the fast flow and close to flood conditions. This is almost certainly due to run-off from agricultural land and from other natural sources. Even in the tidal section, nitrate levels were significantly higher than usual - for example at Lime Kiln Quay in Woodbridge nitrate was 60 ppm this month compared to 15 ppm in February 2025.

By comparison, levels in the Fynn and Lark were similar to the recent trends, with only one or two sampling points showing any increase at all over the previous month.

4. Ammonia

With river levels higher than in previous months and with faster flow, it is not surprising at ammonia levels recorded are low and mainly within WFD guidelines for “good ecological status”. There were two outliers outside the usual Anglian Water outfall sampling points. One at Aspall (Valley Cottage) where the 1.12 ppm reading suggests some local pollution source although E.coli levels were low. The other at Run Meadow near Martlesham at 0.82 ppm is consistent with the high E.coli recorded there.

5. Dissolved Oxygen

We are starting to build data for a few sites using the newly acquired test meters. For the non-tidal section, results from 10 sampling points on the Fynn/Lark show DO2 readings between 10.5 and 11.5 mg/litre with a similar range from 6 sites around Brandeston. By contrast, the two Ufford sites show results around 7.5 mg/litre. The healthy river guideline is 7 to 12 mg/litre indicating the the Deben is in better shape than many other UK rivers.

Check out our River Deben Water Quality Dashboard for detailed results by

location.