environment chiefs are taking urgent action to counter the growing menace of trees alongside one of Hampshire's historic canals.

The Environment Agency says the unrestricted growth of trees is jeopardising the Itchen Navigation that runs from Winchester past Eastleigh to Southampton.

Shade from the trees blocks out sunlight, killing vegetation and driving away animals. The trees eventually become unstable and may fall and damage the banks, allowing water to escape as happened at Allbrook, near Eastleigh, earlier this year.

Now the agency is to launch a ten-year programme to enhance the environment by cutting down many unmanaged trees and pollarding others to stabilise the banks and reintroduce sunlight.

That would encourage the growth of floating vegetation such as ranunculus, crucial for many water creatures.

Rod Murchie, the water resources manager at the agency, said the River Itchen was a site of special scientific interest and special area conservation, and in many places trees were actually damaging wildlife interest.

Mr Murchie said: "Everyone likes trees, but they are a real danger to the public and the structure of the Navigation."

The agency has commissioned consultants who have proposed a programme of remedial works.

The first work will start this winter at the worst-affected areas at Kingfisher Lodge and downstream of Allbrook Lock. Over the next ten years many trees will be chopped down and others pollarded or coppiced. The work may be controversial in places, but the agency is hopeful the public will understand the important reasons.

The removal of many trees will begin to reintroduce the more open 19th century landscape when the water meadows by the navigation were farmed.

The Itchen was first used by commercial traffic in the Middle Ages. The Navigation opened in 1710, and had 17 locks, running up to Wharf Hill in Winchester. The arrival of the railways killed off the waterborne trade in 1869.

Meanwhile, agency workers are restoring the flow to part of the Navigation for the first time in five years.

At Hockley, they are repairing the canal bottom to protect the water flow which is flowing for the first time since the M3 was completed in 1994.