Charlie Downer: Unaware of the dangers

As TV and the media promote the appeal of gardening, enthusiasts are getting more adventurous, introducing ponds and water features.

But hundreds of gardeners are unaware that some imported aquatic plants can have devastating effects if they get into the wild by mistake.

Gardener Charlie Downer says that he did not realise weeds could do damage.

"I built my pond fifty years ago, I put ordinary weeds in and they were suppose to give air to the fish. I didn't know some weeds were dangerous", he said.

Among the non-native plants causing most concern are Australian stonecrop, floating pennywort and parrots feather.

It seems when gardeners clear them out of their ponds, they inadvertently introduce them into the wild where some grow at rates of around 15cm a day.

Martin Harper: "they hog sunlight and oxygen"

It costs around �5m each year to try to clear affected waterways. Conservation groups want the government to ban the sale of some invasive non-native plants.

Martin Harper of Plantlife, a wild-plant conservation charity, says that they must be tackled.

"This foreign invader basically hogs the sunlight, hogs the oxygen and it takes the nutrients away from some of the other species of wild plant in a pond.

"If nothing was done you'd be left with a dense mat and the consequences on the wild plants and on the invertebrates on which they depend would be dramatic", Mr Harper explained.