There has been extensive fish mortality along the twin rivers, this is part of a wider problem affecting various catchments across London. Heathrow Airport  is responding to this problem.

Firstly it is well known that rivers can suffer from low oxygen events when you have a storm event following a period of warm, dry weather. Monitoring on both the Dukes and the Longford showed a low oxygen event entering the Twin Rivers on the afternoon of Saturday 4th July and extending into the evening, oxygen levels then recovered shortly afterwards. This is consistent with a low oxygen event impacting the River Colne catchment following the storms in the early hours of the morning, which then enters the Twin Rivers later that day. It also significant that the water temperature remains high at circa 21C. As fish are cold blooded creatures, their respiration rate increases as the temperature rises. There is also a physical effect that means oxygen is less soluble in water as temperature increases. This creates a vicious circle in such summer storm events as the fish need to breath faster as less oxygen is available.

Heathrow Staff walked the rivers together with the Environment Agency over the weekend and found dead fish along the section they manage. Whilst there is no suggestion that these fish were killed by anything other than a natural event, they have arranged for  contractors to remove the bodies for safe disposal as soon as possible.  

On a more positive note  some fish had survived this event, mainly in the area adjacent to the south west corner of the airport.  Heathrow Airport have been using a tanker to suck water out of the river and spray it into the air to create a small refuge area by re aerating the water. Readings were taken and this appears to have succeeded at a local level.


Design by LTD Design Consultants and build by Garganey Consulting. From an original concept by the Herts and Middlesex Wildlife Trust.