River Chess Association

On 3rd October, we received a call from Thames Water telling us they had detected a spike in ammonia levels in the effluent from the Chesham Sewage Treatment Works (STW).

The impact on oxygen levels is a concern for the health of wildlife in the river. On the same day, we surveyed a 1 mile section of the Chess below the STW outfall and fortunately did not find wildlife in distress. We carried out a riverfly survey to check abundance and varieties of invertebrates in the river and the results are normal for this time of year. We  also tested water quality and reviewed data collected on a 15-minute basis. The data do indicate fluctuating, high levels of ammonia. We will continue to monitor this and be in contact Thames Water until levels stabilise.

Thames Water said, "Over the past few months we have been working on an important project to increase the capacity of Chesham STW. We were configuring the new set-up over the weekend and had some technical issues with part of the treatment process. This meant that we unable to treat ammonia to our normal high standards, which in turn caused pollution to the river. We self-reported this to the Environment Agency and they will be undertaking an impact assessment. Our teams responded quickly and have been working hard to rectify the issue, increasing treatment capability and reducing the impact to the watercourse as rapidly as possible. We care deeply about protecting the River Chess and are working with the River Chess Association to monitor and sample this stretch of river."

With dissolved oxygen levels below 60% for most of the following day, Thames Water has been aerating sections of the river and the Environment Agency have been monitoring fish stocks. After some improvement, ammonia levels began to rise again today, with a concommitant decrease in dissolved oxygen. We are talking to Thames Water about why this issue is on-going.  

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