7th July 2025 Environment Monitoring Results

Deben Climate Centre
Jul 16
3 min read

On July 7th our team of citizen scientists were out along the Deben doing their monthly water quality testing. This month we have some more in depth E.coli observations due to a pollution incident on the Deben, as well as our usual broader results.

Photograph of the River Deben at woodbridge at high tide, looking towards the Tide Mill in the distance. “Woodbridge Suffolk” by Martin Pettitt, CC BY 2.0, cropped. — “Woodbridge Suffolk” by Martin Pettitt, CC BY 2.0, cropped.

1. E.coli

Looking at feedback about the weather over the past weekend, it is clear that some parts of the Deben catchment (e.g. Debenham and Brandeston) only had about 10 mm of rain on Sunday whilst others - such as Woodbridge - reported periods of "torrential rain” that day. However for many places there had been almost no rain for weeks so the weekend rain impact does not account for many of the numbers we are seeing this time.

Below is our usual map which clearly shows the alarming Fynn and Debenham numbers along with the E.coli pollution surge in the Woodbridge area.

Map of environmental monitoring results for E.coli along the River Deben. Results are represented by dots, green dots represent Environment Agency guideline safe bathing at a maximum of 9 colonies per ml, orange dots represent 10-45 colonies per 1ml, and red dots represent more than 45 colonies per 1ml.

Less than a third of the dots on this month's map are green, and all the dots along the Fynn are red.

Note 1: Debenham - 13 samples ranging from 15 to 500 colonies per 1ml: 3 sites not sampled - see separate map

Note 2: 5 tidal samples - 170, 34, 51, 300 and 160 at Woodbridge and Melton - see incident Report.

a). Woodbridge / Melton E.coli Pollution Incident

The extremely high levels of E.coli in the tidal section from Deben Mills Sluice in Melton right down to Kyson Point the southern end of Woodbridge are almost certainly due to the 41 hour storm overflow release which polluted a large section of the river for some days. Although we have not had any confirmation from Anglian Water, their spill map clearly shows this release running from late Sunday until mid-Tuesday. We alerted both the Environment Agency and Anglian Water to the impact downstream and have requested a full investigation and explanation; this is now in hand with the Environment Agency.

We in tandem with the Save the Deben group tested the water in Woodbridge on Tuesday 8th and again on Wednesday 9th; we found significant E.coli presence on both days. At Woodbridge Town Steps on Tuesday the level was 37 colonies per 1ml at noon; at 7.30 pm on Tuesday we recorded 32 colonies per 1ml at River Trips Quay with 9 colonies per 1ml at the Deben Yacht Club. By Friday morning all the pollution had passed. Fortunately, the immediate impact at Waldringfield, Ramsholt and Bawdsey was negligible showing yet again the power of tidal dilution in our river.

Find out more in our previous post: Woodbridge and Melton - Storm Overflow Incident on 6th, 7th and 8th July 2025

b). River Fynn and Lark E.coli spikes

The second area of concern are the results from the River Fynn and Lark; we have seen quite high levels of E, coli coming from the Henley and Tuddenham STW’s in the past. These are small and often ageing sewage treatment works which have previously been overwhelmed in extreme conditions (e.g. Storm Babet). But the weekend rain does not fully explain the red status which applies to almost all the sampling points here.

c). Debenham spikes and Brandeston stretch

There was relatively low rainfall in the Debenham area where the river had been dry previously with a series of stagnant puddles. The limited rain effectively washed pollutants from these and so created a high E.coli impact further downstream. By contrast the E.coli levels from Framsden all the way through Brandeston to Letheringham are much the same as in June

Map of environmental monitoring results for E.coli along the River Deben around Debenham. Results are represented by stars, green stars represent Environment Agency guideline safe bathing at a maximum of 9 colonies per ml, orange stars represent 10-45 colonies per 1ml, and red stars represent more than 45 colonies per 1ml.

All are red with the exception of two orange and 3 blank stars (indicating flow was too low to take an accurate reading).

2. Phosphates

By contrast the phosphate picture is broadly similar to that in recent months. Anglian Water untreated locations (those without phosphate stripping investment such as Easton and Rendlesham) continue to show very high high phosphate levels and this is again notable in the Rivers Fynn and Lark where no investment in these STW’s has taken place. The Wickham Market STW is marginally over its permit limit again this month, which is a concern, particularly as its sister STW’s at Charsfield and Debenham are well within permit.

Map of environmental monitoring results for Phosphate along the River Deben. Results are represented by dots, green dots represent Natural England guideline ‘healthy river’ at a maximum of 0.1 mg/litre, orange dots represent 0.11-0.99 mg/litre, and red dots represent at or above 1 mg/litre.

Less than a third of the dots are green (none along the Fynn), with the rest a mix of red and orange with a skew towards orange.

Note: Debenham - 13 samples ranging from 0.06 to 1.04 mg/litre - see separate map.

Map of environmental monitoring results for Phosphate along the River Deben at Debenham. Results are represented by dots, green dots represent Natural England guideline ‘healthy river’ at a maximum of 0.1 mg/litre, orange dots represent 0.11-0.99 mg/litre, and red dots represent at or above 1 mg/litre.

The majority of dots are orange with one red and one green, there are also 3 dots that are blank (indicating flow too low to take an accurate reading).

3. Nitrates

Nitrate levels are again similar to those in June. As usual, nitrate spikes occur at all the Anglian Water STW’s; there are some high numbers in Debenham mainly due to the concentration of minerals in stagnant pools.

Bar graph showing nitrate levels in the non-tidal River Deben - 2nd June 2025.

The graph features an orange line indicating borderline nitrate levels over 25 ppm, and a red line indicating excessive nitrates over 50 ppm.

The majority of readings are below the orange line, with 6 peaks over the red line, four of which are above 225ppm. These peaks are all located around Sewage Treatment Works (STW).

Bar graph showing nitrate levels in the Rivers Lark and Fynn - 2nd June 2025.

The graph features an orange line indicating borderline nitrate levels over 25 ppm, and a red line indicating excessive nitrates over 50 ppm.

The majority of readings are around the orange line, with 2 at the red line, and 2 significant peaks to 100ppm at Henley and Martlesham.

4. Total Dissolved Solids

We have included a chart showing Total Dissolved Solids (TDS) in the non-tidal River Deben. TDS measures the concentration of inorganic and organic solids in river water; the “normal river range” is between 300 and 1000 parts per million (ppm). You can see from the attached chart that the STW’s all have elevated TDS usually around 1500 ppm or more. The anomalies with levels up to 3000 ppm are in the Debenham / Aspall area where no flow and extensive periods without rain have led to concentrated and stagnant conditions.