The Environment Agency is gathering data and putting together the evidence supplied to them to understand what impact the burst main had on the river. There were dead fish reported from Haxby down to Foss Islands, as well as other seen struggling to breath in the lower reaches.

It is difficult to be sure at this stage how much the pollution contributed to the very low dissolved oxygen levels at different points along the river, and how much was due to the blanket of duckweed: it is likely that it was a combination of the two in some places. Certainly, aeration of the river, arranged by the EA using four pumps, alleviated the situation, and they were switched off after 3 or 4 days when oxygen levels recovered.

A smaller but still significant leak, by Earswick Village, from a completely different part of the system only a few weeks earlier, cannot have helped the situation. Due mainly to high nitrogen levels, the Foss is very much on a knife edge, and incidents such as these are a real worry.

Whilst the investigation continues there is little that can be done apart from keeping an eye on the fish stocks which are currently very visible due to the very low water levels. Reports suggest that there are still plenty around in the lower reaches, whilst in the stretch just below the burst there are none.

The RFS will carry out some checks on invertebrates living on and in the riverbed in a few weeks’ time, once things have settled, and repeat them in the spring to assess their recovery. Any reports of fish seen in the river would be a welcome addition to our monitoring.