An environmental group described “nervous nights” after a fault at a water treatment centre caused a spike in levels of a toxic chemical in river water.
“Technical issues” during expansion at Thames Water’s Chesham Sewage Treatment Works on October 3 led to high levels ammonia posing a threat to wildlife in the River Chess.
The River Chess Association posted on Facebook that day that it had been informed of the leak by Thames Water, and that “the impact on oxygen levels is a concern for the health of wildlife in the river.”
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The wildlife group carried out checks for wildlife in distress, surveying numbers of river flies and varieties of invertebrates.
While results were normal for the time of year, water quality tests indicated fluctuating high levels of ammonia.
The following day, the group reported high levels of ammonium had impacted dissolved oxygen in the water, affecting fish and invertebrates.
The group monitored both and said so far problems had been avoided, with Thames Water aerating sections of the river and the Environment Agency monitoring fish stocks.
They added: “We are not out of the woods and have another nervous night ahead of us.”
And on October 5, the group shared new concerns. A post read: “This water quality issue in the Chess is a bit of a rollercoaster ride. No sooner are we encouraged by improvements than levels of NH4 Ammonium start to rise.”
Describing falling oxygen levels as amounts of the toxin rose, they added: “We are speaking with Thames Water to understand why this has not yet been resolved.”
In an update on Wednesday, the group said water quality in the Chess was almost back to normal, adding: “We continue to monitor water quality and the long term impact on wildlife.”
Thames Water reported itself to the Environment Agency when it discovered the spike.
A spokesperson said: “Operational issues at Chesham sewage treatment meant that we were unable to treat ammonia to our normal high standards, which in turn caused a pollution to the river.”
The company added that it “worked hard” to increase treatment capability and reduce the impact as “rapidly as possible” and said ammonia and dissolved oxygen levels are now back to normal with aerators, used to tackle ammonium, stood down yesterday (October 12).
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