March 3rd 2025 Environment Monitoring Results

Here are the results from March 3rd “sampling safari” with commentary on the findings. The weather that day was sunny, though after a hard frost water temperatures were still around 6 to 7C. River levels appear to have subsided over the past month and the water is clearer than for some months past.

1. E.coli - this month’s E.coli levels are well down on both the January and February numbers at most of the Deben catchment sampling points except for those at the Anglian Water STW outfalls. 

The impact of downstream dilution in the non-tidal river is more marked than over the past 6 months. It is good to see that outside the STW’s there are very few sampling points where E.coli is at anything like the "unsafe level”. This is also very noticeable in the upper reaches around Debenham and Aspall where E.coli spikes occurred in some feeder streams in recent months.

In the tidal section, most of the samples showed low levels of E.coli, By contrast, there was a spike at Kyson Point in the tidal section where E.coli was at 25 colonies/ 1 ml against the February 4 colonies /1ml and January 7 colonies/1ml. The Environment Agency guideline is that for “safe bathing”, the maximum is 9 colonies per 1ml. All three samples were taken on a falling tide and the spike may well be due to the very high E.coli emissions coming out of the Martlesham Creek STW (over 1000 colonies/1ml - over 100 times the “safe to bathe” level). 

This incident reinforces the need for regular / weekly monitoring during the swimming/ sailing season. It also points to the urgent need for Anglian Water to reconsider the case for investment in disinfection/ UV investment at Martlesham to avoid risks to Waldringfield’s "safe bathing status". 

The two maps attached show the E.coli levels by location.

2. Phosphates - it is good to report that phosphate (as P) levels have generally fallen by comparison with previous months. For the River Deben, the Easton and Rendlesham STW’s now appear to be the only major sources of phosphate pollution in the main river. It is very noticeable that from Debenham downstream, almost all sampling point readings were within the Natural England 0.1 ppm (mg/litre) guideline for a healthy river. 

This is major change from 12 months ago when phosphate emissions both from STW’s and from agricultural sources had a significant impact on water quality. Perhaps the most marked change is at Charsfield/ Potsford Brook where Anglian Water invested in phosphate stripping technology in late 2024. From a high point 12 months ago in April 2024 phosphate at 5.15 ppm has fallen massively to  0.07 ppm (a fall of over 50 fold in 12 months). In the Debenham/ Aspall area, phosphate levels are some of the lowest we have recorded since phosphate testing began over 18 months ago. 

By comparison, the River Lark and Fynn still show quite high phosphate levels, though lower than in recent months. There are several small STW’s on these tributaries which are not judged by the Environment Agency/ Anglian Water to be worth the phosphate stripping investment. Perhaps it is time to reassess this position.

3. Nitrates - nitrates are an important pollutant with both waste water and agricultural activities being important sources. The attached chart shows that, in the past month, and contrary to the phosphate level reduction, nitrate levels appear to have climbed across several locations between February and March. 

Around half the samples showed nitrate levels above the 25 mg/litre NO3 “borderline” Water Framework Directive guideline. However, the “excessive” samples were mainly from STW outfalls or from smaller streams. One factor may be that landowners have been working on seasonal ditch clearance and tree removal adjacent to and in the river; this in turn may have led to short-term increases in nitrate leaching.

More work is needed to track nitrate pollution over the coming months. We know that several of the local landowner groups and “farm clusters” are looking at nitrate reduction opportunities; these data reinforce the need for action and for intensive monitoring..

My thanks to all our volunteer samplers who do a great job both in sampling but also in recording a much wider range on river characteristics than can be shown in this Report.