‘Tenchsion’ mounts as British Waterways evicts big fish from small pond

28 January 2009

Big fish in small pond stir up trouble for their delicate neighbours.

British Waterways is anticipating to relocate more than a tonne of fish from a section of the Kennet & Avon Canal as part of a programme to improve conditions for aquatic wildlife, including dragonflies. The abnormally large number of fish, which have been left to flourish undisturbed for many years, will be removed from the side ponds of the famous Caen Hill lock flight – a ‘staircase’ of sixteen locks – near Devizes in Wiltshire.

The large number of boats moving through the locks stir up silt and so do, perhaps surprisingly, large fish feeding on the bottom of the ponds. This causes the growth of algae due to the subsequent release of nutrients in the water. Over recent years, the water in the side ponds has, therefore, become less suitable for invertebrates such as dragonflies and damselflies, as well as scarce aquatic plants that rely on clear-water environments.

British Waterways ecologists, who are co-ordinating the work, are therefore relocating a proportion of the fish to other parts of the canal network, including the Grand Union Canal. This will restore a more balanced population and reduce silt disturbance, allowing other wildlife to recover. They expect to find large tench, carp, bream, roach, perch and pike as well as eels. Some of the catch will be released onto the Kennet & Avon Canal below the lock flight allowing local anglers a chance to fish for them.

The Caen Hill side ponds were originally designed 200 years ago as ‘holding tanks’ to store the water needed to operate this extraordinary flight of locks, due to the steepness of the terrain. Together, these side ponds represent one of the largest stretches of open water in this part of Wiltshire and are a great wildlife habitat for species including grass snakes, various birds and water voles.

Once the water in the side ponds has been drained down to a level of about two feet, a team of fisheries experts will use 100m seine nets to trap fish before wading in to scoop up the largest. The fish will be carefully transferred into aerated tanks before being transported to their new home.

John Ellis, fisheries manager for British Waterways, says: “We take great care of the fish throughout every part of the process and local anglers will welcome the release of some of these larger fish into the canal. Anglers love the excitement of seeing if they can land a really big carp and this fish operation will certainly bring some weighty specimens to light.”

Oda Dijksterhuis, British Waterways heritage and environment manager, says: “This is a very exciting project for us. By removing these larger fish we hope to see an improvement in the water clarity in the side ponds. This will mean that a greater range of plants and invertebrates will be able to thrive and then, hopefully, some of the once abundant dragonflies will return.”

The project is funded by British Waterways and supported by the Waterways Trust.

In addition to relocating the fish, silt curtains will be put in place across the entrance to one of the side ponds at Caen Hill in a trial to further improve water quality. The curtain will prevent silt stirred up by boats navigating the locks, from entering the ponds.

British Waterways cares for 2,200 miles of the nation's canals and rivers. Rich in heritage, abundant in wildlife and teeming with activity, inland waterways are as popular today as they've ever been. Half the population lives within five miles of one of our waterways and an incredible 11 million people use them every year as part of their everyday life – as a short-cut to work, for walking the dog or simply for taking time-out and watching the boats. British Waterways' job is to ensure the waterways attract enough investment to be well maintained and remain appealing to society and the local communities through which they pass.
www.britishwaterways.co.uk