Debenham Green team stall outside the Lion, November 2024 to present the results of the monthly water sampling of the river Deben at 16 locations in Debenham .

June 2025 Sampling

We completed our latest Deben Sampling Safari earlier this week and here are the results along with a more detailed commentary than usual. 
After a record dry Spring and early Summer with very little rain (only 15 -20 mm of rain has fallen since late February according to one local landowner), river levels are probably at a record low and we were unable to take samples at a number of locations. 

This photo shows the dry stream bed at Charsfield Bridge – about 200 m above the Anglain Water STW outfall – someone has mown the grass and there is no sign of any water!

We added two new sampling sites in the area above Brandeston, giving us almost full coverage of the non-tidal Deben and its tributaries. I have included the key findings with comment here but there is now a lot more test result detail on our Deben Water Quality Tableau website, where we now have over 18 months data allowing you to look at trends for the catchment and specific sites.

1. E.coli – as in May, E.coli levels for most of River Deben were very low, except in the usual hotpots at and below the Anglian Water STW’s. However in the River Fynn and at Debenham, the downstream impact from STW’s combined with very low flows made E.coli levels higher than recently. We were unable to take samples at several locations notably in Charsfield, Framsden and at Debenham. 
Charsfield STW and its downstream locations usually show high levels of E.coli, so the very low numbers this month are against all previous findings here; both nitrate and ammonia were present so it seems clear that the STW was operating. This will need further investigation to see if this is a one-off finding.

2. Phosphate – The phosphate picture is more complex this month due to very low river levels and also to the impact of STW’s where there has been no phosphate reduction investment by Anglian Water. 
Phosphate levels across the River Deben itself were low between Crettingham and Ufford, away from the two STW’s at Easton and Rendlesham, mostly showing levels within the Natural England 0.1 mg/ litre target. By contrast, the Rivers Fynn and Lark showed raised phosphate concentrations due, we suggest, to the fact that the STW’s here are small, inefficient and have had no investment in phosphate reduction. At Debenham, the raised levels are more likely due to very low water levels leading to excess concentrations of minerals. The latter is borne out by our findings on Electrical Conductivity and Turbidity at these locations.
For the second month, the Wickham Market STW phosphate reading is just above its permitted phosphate output; this will be flagged with the Environment Agency and Anglian Water.

3. Turbidity and Water Quality – this chart shows the dramatic effect of very low flows and higher concentrations of minerals resulting from this, coupled with the effect of warm weather. This is  almost exclusively affecting Debenham and the source water near Aspall, where turbidity spikes. Lower down the river, the water is much clearer although our Electrical Conductivity readings were generally higher this month than in the previous 3 months 

4. Impact of Very Low Flow and Warm Weather – our samplers and local landowners have reported that the river appears to have a more brackish and brown coloration this month although the water still appears clear. Looking at this in more detail, we have identified after advice from the Environment Agency, that this effect is caused by high levels of algal growth. When combined with silt particles, this growth coats the riverbed and the weeds with a green/brown layer which at first sight may look to some like sewage fungus. 
The photo below, taken at Brandeston Ford, shows strands of weed coated in algae. Similar weed was found all along the river especially where the water is open to sunlight, which creates the conditions for fast algal growth.

We are grateful to John Findlay from the Environment Agency for his explanation of what is happening here.

“That’s algae, likely predominantly the wiry Cladophora glomerata/Rhizoclonium heiroglyphicum species pair. It develops a slimy feel as it tends to become covered with a film of silt and bacteria. It isn’t good news as it will blanket the riverbed, changing the available habitat and potentially restricting the flow of water and thus oxygen into the riverbed. It is however a natural or semi-natural occurrence in sunny, low flow conditions as such conditions concentrate nutrients and mean the algae is likely to be growing in clear shallow water and so getting plenty of light. Reductions in flows due to abstraction, increased nutrient loads from anthropogenic sources and unusually warm dry weather because of climate change all have the potential to increase the extent of algal growth and the bacterial films that cover it. The algae will likely die back later in the year.”5. Deben Water Quality Tableau Dashboard – further work has now been completed to add Deben Climate Centre water quality data from the whole of 2024 into the Dashboard. Our policy is to enable “open access” to all the data, so allowing wider understanding of what is happening in the Deben .

6th May 2025 Sampling Results from Deben Climate Centre

Here are the results from this week’s sampling across the Deben catchment. With the dry and sunny weather, some sections of the river were static and in places completely dry. In others the concentration of minerals in the water was significant leading to Electrical Conductivity numbers well outside normal river boundaries. Conversely, expect at one or two notable points – mainly AW sewage outfalls – phosphate and nitrate levels continue to be lower than for many months. This probably down to the lack of run-off from agricultural sources given the lack of water in ditches and feeder streams.

This month, we have a number of new sampling points on the section between Brandeston and Debenham, building on the work done in mid-April to cover this important section. Thus far the Deben water quality results from here show no cause for concern.

1. E.coli – we found the usual pattern of very high E.coli at the Anglian Water sewage works outfalls and just below these. In many other locations, particularly in the tidal estuary and above Easton E.coli levels were minimal. At Debenham, low river levels contributed to some hotspots where usually there is little or no evidence of E.coli pollution.

The outfall pipe close to Woodbridge Station, discovered in April following a tip-off from the Harbourmaster, proved to be a serious hotspot again with 300 E.coli colonies per 1ml (this is close to the Martlesham Creek numbers but with much lower flow). This suspicious outfall is being reported again to the Environment Agency as it doesn’t appear to be associated with any Anglian Water or other licensed activity.

2. Phosphate – the phosphate results are broadly similar to those in March/ April, with low levels for the vast majority of sampling points. 

As usual the Rendelsham STW continues to emit high phosphate levels (5.02 mg/litre) and even 500 metres downstream at Naunton Meadow, the concentration are still very high (1.11 mg/litre). These compare badly with the Natural England “healthy river” target of 0.1 mg/litre. The River Fynn Henley sample taken close to the STW outfall was even worse at 7.44 mg/litre. 

At Wickham Market, where phosphate stripping has been installed we found the outfall phosphate level just over the Environment Agency Permit level – 1.04 mg/litre as against the Permit at 1.0 mg/litre; this will need careful monitoring to see if this small deviation is repeated.

We have had some welcome news recently about the Rendlesham phosphate situation. Following a meeting between senior Anglian Water management, Sir Michael Bunbury – the local landowner – and representatives from the Deben Climate Centre and River Deben Association, we have been given a commitment by Anglian Water that the Rendlesham phosphate stripping investment will be brought forward into the “first tranche for installation planning”. This means that instead of a the March 2027 permit date, we can expect the investment in this 2025/26 financial year. We will know precise dates soon.

3. Nitrates – nitrate levels continue to be low in spite of the dry weather and lower flows. Only the STW outfalls on the Deben show any significant nitrate presence; there was a similar picture on the Fynn and Lark

4. Deben Water Quality Data – NEW: Tableau Public mapping and data analysis – over the past few months, we have been working with Friends of the River Wye, a well-known citizen science group, to develop a better set of mapping and analysis tools. We are very fortunate that Michael Carpenter, their lead on mapping and analysis, has helped to adapt their visualisation and trend mapping tool with us.Using the tried and tested Tableau Public data visualisation tool, we have created a Deben Water Quality Data tool to allow public access to the Deben Climate Centre water quality data. The database covers the period from October 2024 when we started to gather more extensive information about the river state, such as pH, temperature, turbidity and electrical conductivity as well as the test results for E.col, phosphate and nitrate. 

There are hundreds of other applications which use Tableau Public and several cover water quality elsewhere in the UK and the wider world.A link to our Tableau Public tool is attached below; simply click on the link here and this will take you to the Deben Water Quality Data page. 

https://public.tableau.com/app/profile/david.findley/viz/DebenWaterQuality_17453989430370/Title

31st March 2025 Sampling Results from Deben Climate Centre

Here are the results from this week’s sampling across the River Deben catchment. March has been one of the driest months on record for East Suffolk with almost no rain in many of our sampling locations. Anyone travelling around will see the impact in the fields with bone dry soil or with the need for irrigation on recently planted crops. Equally at some of our sampling locations, the weather conditions have led to dry riverbeds or to very slow flow. 

These conditions have had quite a dramatic effect on some of the results we are reporting, making interpretation rather challenging. 

We are reporting additional features this month to try to explain what seems to be happening in the catchment. So there is lot more to read and absorb in this bulletin.

1. E.coli Results – across the non-tidal catchment E.coli levels have dropped relative to February and earlier in March. The only exceptions are at or close to the Anglian Water sewage outfalls where E.coli emissions continue at high levels. It is noticeable that there are only a few “orange” indicators on the map with many locations showing no E.coli presence at all. One possible explanation is that with no significant rain, ditches and small streams have run dry and so there is no run-off into the river. Hence almost the only E.coli sources are from the AW STW’s or from private outfalls.

In the tidal section, there was a spring high tide on the day of sampling and E.coli levels were very low (except at Martlesham Creek). Some observers we spoke to had expected high levels due to wash from river banks but there is no evidence of this at all. The one outlier is a newly discovered outfall into Woodbridge houseboats are where E.coli levels were well above “safe”; the local harbourmaster had reported a sewage smell so we are going to monitor this pipe in future.

2. Phosphate – across the catchment levels of phosphate pollution were generally about the same as those for the previous samplings in February and March. The Anglian Water STWs with phosphate stripping installed all showed levels within 0.5 ppm and are well within the Environment Agency permit limits. The outliers at Rendlesham and Easton on the River Deben, at Henley on the River Fynn and at Martlesham Creek in the tidal section all  emit phosphate at 30 to almost 70 times the “healthy river” guideline. A meeting with Anglian Water about the Rendlesham phosphate issue is expected soon.

3. Nitrate – this month’s results show quite a dramatic drop in the level of nitrates in much of the River Deben, compared to February and March. The majority of results are within the 25 ppm limit set by the Water Framework Directive with many being at 10 ppm or less. One explanation is that nitrate leaching from agricultural sources and outflow from ditches has been negligible due to the lack of rain; the spikes on the chart attached are all from AW STW outfalls. Nitrate levels in the Rivers Lark and Fynn are by contrast relatively similar to earlier numbers.

4. Electrical Conductivity – measures the presence of inorganic dissolved solids (salts) in water. Conductivity is a good indicator of water quality and is measured in milliSiemens (mS). For normal river water the expected range is 0.3 to 1.0 mS. However for streams coming from clay soils, levels are higher due to the presence of materials that ionise when washed out by water. Similarly water from chalk aquifers have higher conductivity. Waste water from sewage treatment works also shows high electrical conductivity due to the presence of inorganic compounds (e.g chlorides, sulphates and nitrates) in emissions. Sea water with its high sodium choline (salt) content registers very high conductivity (over 10 mS).

For the River Deben, most samples are within the expected range with STW emissions being significantly higher. The samples from the source streams at Debenham and Aspall all show elevated electrical conductivity with many being over 2.0 mS. This may be explained by the clay soils and by the static or very low flows observed; the latter leading to concentration of minerals in the water. The samples for the Rivers Fynn and Lark are broadly within expected levels, although those closest to the Martlesham sluice show elevated numbers probably due to the intrusion of saline water at high tide.

Our evidence to date suggests these results can help us to quickly assess the river water quality on-the-spot without resort to detailed tests. Broadly the higher the electrical conductivity the more likely there is to be a pollution incident or other feature worth investigating. But care is needed to take account of the local geology and spoil types.

5. Total Dissolved Solids (TDS) – this measure is somewhat similar to electrical conductivity and measures the presence of dissolved organic and inorganic materials in the water. The primary sources of TDS in rivers are from farm and residential run-off, from soil leaching contamination and from sewage treatment plants. The expected range for rivers in good health is 300 – 600 ppm of dissolved solids; 900 – 1200 ppm is rated as poor and any reading over 1200 ppm is deemed unacceptable.Our analysis suggests that almost all the River Deben catchment samples show TDS levels at or above those for a “health river” (so in the range 600 to 100) with some well above this. The numbers for earlier in March are somewhat lower suggesting that the lack of rain and the low flow have contributed to a concentration of these materials in the water. However, the lower nitrate levels run counter to these results, so more data is needed from future months to understand the trends.