Some time ago a member of the London Fishkeeping Club as mentioned going up the Thames looking for plants or pieces of wood. I thought that it was a weird idea, after all, what sort of plant would we find? The water would either be too cold or too dirty. Well, maybe I should definitely take the time to go for a walk on the water side. Taken from the Telegraph article: Crassula helmsii spreads vigorously, having weak stems that can break into tiny sections, each with the ability to root and grow. These fragments can be transferred to new sites by birds or animals - or people. Its unusual physiology also enables it to grow rapidly for up to 20 hours a day, without a dormant season. It forms a dense mat of vegetation that out-competes native waterplants and can cause severe oxygen depletion, threatening wildlife and rare plants such as the starfruit Damasonium alisma. Ironically, New Zealand pygmyweed was introduced as an "oxygenator", but instead has become a strangling monster. The second plant in the unholy trinity is a South American native, the parrot-feather (Myriophyllum aquaticum). Closely related to the British water-milfoils, it became naturalised here in about 1970. As with Crassula, it grows rapidly and produces many adventitious roots but it is more likely to be dispersed by discarding or deliberate planting than by chance. It has whorls of attractive ferny leaves that emerge from the water. Now found at more than 100 sites in Britain, it overwinters as a rhizome. It too infests waterways. The third and most recently introduced villain is the floating pennywort, Hydrocotyle ranunculoides, which again has a close British relative, marsh pennywort (H. vulgaris). First recorded in 1990, this North American native has already spread to more than 40 sites, mainly in the south of England and Wales, and looks set to become a serious problem. http://www.telegraph.co.uk/gardening/47 ... aders.html Now, do you where we could find some of these alien invaders? It would be really cool to setup a cold water plant tank.