We also have extensive areas affected by Himalayan Balsam and Japanese Knotweed.
Himalayan Balsam may have pretty pink flowers but it blankets the land where it grows and blocks out any other form of vegetation. So it reduces biodiversity and in the winter the barren ground is more susceptible to being washed away in floods. We regularly run volunteer events clearing this weed, but you can easily pull it out yourself.
Japanese Knotweed was originally introduced by a plantsman from Leeds (!) and will grow through tarmac and even some layers of concrete; it has even appeared inside houses where it grows adjacent to walls! As with Himalayan Balsam, it totally blankets the ground where it grows. It can be removed by persistent cutting back over several years or by stem-injection of a commercial herbicide - if you need our help to do this then please contact us.
As well as the issues with vegetation mentioned above, we are concerned about the spread of the American Red-Clawed Crayfish.
This import is taking over our rivers and driving out the native White-Clawed species. The invader is bigger and can out-compete the native for food, moreover it carries a fungal disease that can be fatal to the native. All in all a bad deal and, if truth be told, it's possibly a lost battle although efforts are being made to protect the last few locations where only native crayfish can be found.