ALIEN killer weeds are threatening to choke the life out of North-East waterways unless they are stopped, say environment experts.

Species from Asia and North America strangle the natural vegetation, damaging local ecology in ponds, lakes, marshes and watersides.

The problem has got so bad on Wearside that Sunderland City Council has launched a weed strategy to combat it.

Claire Dewson, council countryside officer, said: "Noxious weeds are destroying our riverside habitats. It is actually a criminal offence to allow or knowingly spread any of these species."

The main culprits are giant hogweed, Japanese knotweed, Canadian pondweed and crassula helmsil, better known as Australian swamp stonecrop.

"One small fragment of any crassura can spread like wildfire and we have to stop its spread before it is too late," said Ms Dewson. "We would urge people to report any sightings immediately."

The problem is being blamed on people buying the weeds for garden ponds or aquariums, then dumping them by tipping water into streams. Other weeds to look for include water fern, minute duckweed, parrot's feather and floating penny wort.

For further details about the weed strategy, call Sunderland's countryside team on 0191-553 1555, or visit the website, www.sunderland.gov.uk/ countryside