[CUCBC Coxes] Possible river pollution

[Conor Burgess]

Hi all,

The Environment Agency now believe the source of the dead fish was likely a localised area of very low dissolved oxygen, and that the heavy rainfall led to this poor quality water and the dead fish being washed downstream, which would explain why the dissolved oxygen content in the river measured on Tuesday (50%) was low, but not so low as to cause the fish deaths directly (the fact there were healthy fish observed in close proximity to the dead fish supports this too). They measured the dissolved oxygen levels back up at 100% on Friday, so the river seems to be recovering. The dead fish are expected to be washed down to the weirs where they will decompose, but the aeration of the water at the weir should counteract the reduction in dissolved oxygen which occurs with decomposition.

There is therefore no evidence that the river contains anything more harmful than it normally does, but Leptospirosis (Weil’s Disease) is always a risk, so please remember to always wash your hands after outings etc.

Best wishes,
Conor
On 23 Jun 2023 at 11:48 +0100, Conor Burgess <conor at cucbc.org>, wrote:
> Dear all,
>
> Thus far, no specific cause for the fish deaths has been identified - the tests have not identified any pollutant to explain them, nor were the dissolved oxygen levels in the water samples taken on Tuesday low enough to provide an explanation.
>
> The Environment Agency will be back on the river taking further samples to measure the dissolved oxygen levels today (Friday 23rd). One possible explanation is that the large amount of cold storm water entering the river from the heavy rains led to the dissolved oxygen levels in the warmer river water becoming so low as to cause the fish deaths, as cold water can dissolve oxygen better than warm water. Unfortunately the results of the tests on Tuesday cannot prove this, so for now, please continue to take extra precautions after outings.
>
> Best wishes,
> Conor
> On 21 Jun 2023 at 12:13 +0100, Conor Burgess <conor at cucbc.org>, wrote:
> > Dear all,
> >
> > Sadly a large number (~1000) dead fish have been found in the Cam between Chesterton and Baitsbite Lock. It is possible that a pollutant may be the cause, and the Environment Agency and Anglian Water are investigating / testing water samples etc.
> >
> > Even more so than you usually would, please ensure all of your rowers and coxes limit their exposure to Cam water (i.e. washing equipment and then hands after outings, avoid novice sculling sessions where capsizes are more likely, etc.), at least until we know more about what has killed the fish.
> >
> > Best wishes,
> > Conor
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