Kennet pollution: fish 'ill equipped' for winter

The warning came from an Environment Agency (EA) team using ‘electrofishing’ equipment this week to stun their quarry in order to weigh them and check their health.
The pollution was first discovered on July 1 by volunteer riverfly monitors working for Action for the River Kennet (ARK).
Investigations by the EA revealed the culprit was a lethal insecticide identified as chlorpyrifos.
As little as a few teaspoonsful are thought to have entered the watercourse from a water treatment works in Marlborough, Wiltshire, leading to a 15km stretch of water down to Hungerford being affected.
The River Kennet is a Site of Special Scientific Interest (SSSI) and one of England’s finest chalkstreams. The incident is one of the largest ever and wiped out insect life – a major source of food for fish and other wildlife – in around a third of the river.
The agency’s fisheries team leader, John Sutton, said yesterday (Wednesday): “Although, to our knowledge, no fish were killed, we wanted to assess the condition they were in after their regular food supply was wiped out. Are they losing weight or are they managing to find a living?"
His team, working alongside ARK volunteers and scientists from University College in London, isolated river sections using nets placed 50m apart.
They then deployed ‘electrofishing’ wands. Mr Sutton explained: “They generate an electric current that affects the fish’s nervous system, momentarily stunning them.”
The fish are then scooped up in nets and placed in oxygenated water tanks where they are weighed and examined before being returned, unharmed.
Mr Sutton said: “We will have to wait for the full results but anecdotal evidence suggests many fish are thinner than expected and therefore not well equipped to cope with winter, when things will get tougher.
“However we were encouraged to see the full range of expected species including the five main ones: brown trout, grayling,
brook lamprey, bullheads and sticklebacks.”
He added: “We noticed that, even three months after the incident, a cursory glance was enough to see a huge absence of common aquatic invertebrates such as shrimp. It’s likely that the fish have been surviving on mainly terrestrial insects such as hoverflies and midgies blown from the bank into the water.”
The team will compare the results with those from routine tests conducted last year and Mr Sutton said: “We will be back next spring to repeat the exercise.”
A 10-mile (16km) stretch of the river in Berkshire and Wiltshire, which is a Site of Special Scientific Interest (SSSI), was affected.
The source of the contamination was never found.