1st December 2025 River Deben Environment Monitoring Results
- Deben Climate Centre
- 10 minutes ago
- 3 min read
The past weeks have seen periods of heavy rain and river levels have returned to the norm for the season we are in. Indeed, the flood plain below Wickham Market has been quite waterlogged and has had minor flooding a couple of times in November.
This week our Citizen Scientist volunteers have been braving the wintery weather, sampling across the Deben:
1. E.coli pollution
The past month has seen several CSO spills in the Woodbridge area, after heavy rain showers, resulting in pollution incidents. However when we tested this week there was little evidence of elevated E.coli levels in the tidal section. The exception was Kyson Point with 25 colonies per 1ml, probably resulting from the volume of waste water coming from Martlesham Creek STW.
On the Fynn/ Lark, E coli levels were slightly lower than in November but are still very high downstream of the Anglian Water STW’s. In the non-tidal Deben, the Wickham Market emissions were much high than in previous months and the downstream impact was felt almost a mile downstream at White Bridges. In the Crettingham to Easton area, E.coli levels were minimal - there are few livestock here so any pollution is likely to be from agricultural run-off. There is little evidence of this carrying bacterial pollution whereas the nitrate story is quite different (see below).
There was a similar picture at Debenham, with lower E.coli pollution levels than those seen for some months. This is encouraging especially as in prior years we have seen winter spikes after heavy rain. There is one outlier at Kenton Bridge which needs further investigation.
2. Phosphates
Apart from the two Anglian Water STW’s at Rendlesham and Martlesham which continue to emit high levels of phosphate pollution (at 40 times the heathly river guideline), there has been a drop again in phosphate pollution levels. This is particularly the case on the Fynn/ Lark and in the section above Easton all the way to the source at Debenham.
It is encouraging to note that Anglian Water have taken action at Wickham Market to rebalance the operation of the phosphate removal technology so that levels have fallen from around 1.2 mg/litre back below the permitted 1 mg/litre maximum.
At Debenham, the installation of the phosphate stripping plant has seen the lowest levels of phosphate for almost 18 months. For the whole of this stretch from Brandeston right up to the source waters, we are close to the achieving “good status” on the Deben.
3. Nitrates
Over the past two months nitrate pollution has spiked with many sampling locations showing nitrate levels 3 to 5 times those seen in September. Outside the Anglian Water STW’s, nitrate averages 100 ppm in many parts for the non-tidal catchment. Even in the upper end of the tidal section, nitrates were 25 to 50 ppm this month as against 5 to 10 ppm in September. Levels on the Fynn/ Lark are slightly lower but still much higher than earlier in the year.
It seems that over the past two months, and after a very dry summer, rainfall has flushed large amounts of residual nitrate from the land, from ditches and through field drains all the way along the river valley. This is perhaps no surprise but it also seems clear that the Anglian Water STW emissions play a very minor role in this. Nitrate removal from these STW’s would be expensive and probably unjustified given the above.
4. Ammonia
The presence of ammonia in our river water is a good indicator of sewage and related pollution. We would expect levels to be less than 0.25 ppm and certainly no more than 0.50 ppm; the latter being an indicator of sewage pollution warranting investigation.
For the Deben catchment, we do not yet have full coverage but from 30 samples, the only one over 0.50 ppm came from the Wickham Market STW outfall with an ammonia rating at 6.25 ppm. Others taken at or downstream of Anglian Water STW’s were slightly above the 0.25 ppm limit with the rest being well below that.
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