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2nd March 2026 River Deben Environment Monitoring Results

  • Writer: Deben Climate Centre
    Deben Climate Centre
  • Mar 6
  • 2 min read

Our recent sampling round earlier this week took place in some very welcome sunny spring weather, with river levels having returned to normal after several weeks of high flood-type conditions. As such, comparison of this month's results is best looked at in the context of the late 2025 results rather than those for early 2026.


Photo of the river on a clear day, flowing slowly through trees on the bank
1. E.coli

Bacterial pollution in the River Deben and its tributaries is still significant especially at and downstream of the larger Anglian Water Treatment Works. Although there are some pollution "hotspots" this month, levels have fallen overall for both the non-tidal Deben and the Fynn/Lark tributaries. The Fynn/ Lark has much lower pollution levels than those seen before Christmas especially at the Henley and Tuddenham STW sample points.


In the tidal section, there are a few locations where E.coli levels are still high - Lime Kiln Quay and Melton being two examples. The Kyson Point sample is probably impacted by the high readings at Martlesham Creek.


In the Debenham section, E.coli levels are similar to those seen in the latter part of 2025; the exception is the Aspall Gull Farm sample point which recorded 194 colonies per 1ml. This has been reported to the Environment Agency hotline for their attention, as we suspect a leaking private outfall or similar.

Map of the river Deben showing E.coli levels as described in the text above. Environment Agency guideline for safe bathing is maximum of 9 colonies per 1ml: 21 test sites marked green (9 or fewer E.coli colonies per 1ml) 28 test sites marked orange (10 to 45 E.coli colonies per 1ml) 4 test sites marked red (more than to 45 E.coli colonies per 1ml)
Map of the river Deben at Debenham showing E.coli levels as described in the text above. Environment Agency guideline for safe bathing is maximum of 9 colonies per 1ml: 6 test sites marked green (9 or fewer E.coli colonies per 1ml) 9 test sites marked orange (10 to 45 E.coli colonies per 1ml) 1 test sites marked red (more than to 45 E.coli colonies per 1ml)
2. Phosphate

In most places, phosphate pollution levels have returned to those seen in 2025. The two Anglian Water STW's at Martleham Creek and Rendlesham continue to be the highest emitters, although we recorded a spike at Charfield - over 1.6 ppm - even though there is phosphate stripper in place at this works. 


In the tidal section, we still have concerns about the Kyson Point number - nearly 0.3 mg/ litre - but this is much reduced from the February spike at over 3 mg/litre. We reported this earlier phosphate pollution to the Environment Agency but a point source has not been identified.


The Fynn/Lark readings were considerably lower than in previous months, perhaps due to floodwater washing out accumulated residues.


At Debenham, all but one of the sample points showed phosphate within the 0.1 mg/litre healthy river target; the installation of the phosphate stripper at the local STW continues to have a dramatic local effect.

Map of the river Deben showing Phosphate levels as described in the text above. Natural England "healthy river" is max 0.1 mg/litre Phosphate as P: Environment Agency guideline for safe bathing is maximum of 9 colonies per 1ml: 23 test sites marked green (less than 0.1 mg/litre) 17 test sites marked orange (0.11 to 0.99 mg/litre) 3 test sites marked red (at or above 1 mg/litre)
Map of the river Deben at Debenham showing Phosphate levels as described in the text above. Natural England "healthy river" is max 0.1 mg/litre Phosphate as P: 15 test sites marked green (less than 0.1 mg/litre) 1 test sites marked orange (0.11 to 0.99 mg/litre) 0 test sites marked red (at or above 1 mg/litre)
3. Nitrate

There has been a slight fall in nitrate pollution levels in both the Deben and in the Fynn/Lark tributaries. There are fewer "over 50 ppm" readings in both charts below. As the floods have receded, so the volume of soil runoff and nitrates has dropped away.

Bar graph showing nitrate levels in the non-tidal river deben (NO3 ppm) as described in the text above. 21 results below 25 ppm. 13 results between 25 ppm and 50 ppm (borderline), 6 results between 50 ppm and 100 ppm (excessive), 0 results between 100 ppm and 250 ppm, 1 results between 150 ppm and 200 ppm (max)
Bar graph showing nitrate levels in the river lark and fynn (NO3 ppm) as described in the text above. 3 results below 25 ppm, 7 results between 25 ppm and 50 ppm (borderline), 2 results between 50 ppm and 75 ppm (excessive), 1 results between 75 ppm and 100 ppm (max)
4. Ammonia

We have changed our ammonia protocol to minimise the use of a Hanna test reagent which is toxic, replacing this - in all cases except where a new pollution incident is suspected -  with ammonia test strips. These strips are indicative rather than accurate but are allowing us to test more samples quickly.


The only "hotspots" across the catchment were at Martlesham Creek STW with 50 ppm NH3-N and at Wickham Market with 3 ppm NH3-N. The danger level is any reading at 3 ppm or over. The Martlesham result is being flagged with Anglian Water as this is well above the previous trend line for this large STW outfall.


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

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