3rd November 2025 River Deben Environment Monitoring Results

Thanks to our group of now nearly 50 volunteers, including 6 new volunteers this month, we sampled and tested over 60 locations in the Deben catchment this week.

Although October has seen more rain than in any of the previous 3 months, river levels are still low and many of the ditches and even some feeder streams - e.g Framsden and Potsford Brook - are quite dry. That said, at Debenham all the sampling locations now have water present for the first time in 6 months.

During October, we saw a number of CSO spill incidents in the Woodbridge/ Melton area; most are apparently attributable to short periods of heavy rainfall.

1. E.coli Pollution

The pattern of this week’s environmental monitoring results are broadly similar to the established trends where E.coli spikes are generally associated with Anglian Water’s treatment works.

At Debenham, river levels have recovered and all 16 sites were sampled with E.coli levels close to previous trends. With river levels still quite low and ditches dry in many places, farm runoff is not likely to be impacting on E.coli; this is particularly notable in the section from Debenham to Letheringham. Just downstream, the Easton E.coli numbers are dramatically lower due to our being unable to access the STW outfall directly anymore. E.coli levels on the Lark and Fynn are also lower this month due in part to greater flow in these small rivers.

The two greatest concerns this month are in the tidal section at Ramsholt Quay where E.coli was at 35 colonies per 1ml, nearly 4 times that acceptable level, and at Wilford Bridge with a spike at 49 colonies per 1ml. The Ramsholt spike needs further EA investigation as we have seen similar, though somewhat lower levels before. There has been previous speculation that there may be a leaky septic tank outfall nearby. The Wilford Bridge spike is surprising given the very low level of E.coli recorded at Ufford just a mile upriver.

2. Phosphates

Phosphate levels for the catchment are generally down on October’s numbers, those on the Lark and Fynn by some margin due probably to higher flow rates. 

The outfalls from the Anglian Water works at Henley, Grundisburgh, Martlesham Creek and Rendlesham are the main sources of concern although we understand that the small Grundisburgh works is due to have phosphate stripping investment soon. We are still waiting to hear about the Rendlesham works date. It is good to see that phosphate emissions from Wickham Market are back within permitted levels after several months of reported operational problems there.

Given the tidal dilution in the estuary section, it is concerning to see phosphate levels outside the “healthy river” guidelines. Water users continue to report algal and weed growth affecting sailing boats, most likely due to a combination of nitrate and phosphate pollution.

3. Nitrates

Across the non-tidal catchment, nitrate levels are much higher than the “healthy” level of 5 to 10 ppm NO3 and, in many cases, are on poor status (over 25 ppm NO3).  The exception is the stretch close to the source waters at Debenham; in general the lower reaches between Brandeston and Ufford have much poorer status. A combination of nitrate emissions from the treatment works and from run-off during heavy rain showers experienced in October are probably the main contributors. Nitrate levels will be a particular focus in the next 3 months as rainfall levels increase due to autumn/ winter rains.

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

location.