Your quite right, there are a number of plants that have gone wild and are proving nigh on impossible to control. Crassulla helmsii (Australian Swamp Stonecrop), Myriophylum aquaticum (Parrots Feather) and Hydrocotyle ranunculoides (Floating Pennywort) are three of the most common culprits, even though they are still on sale at some garden centres. Bodies such as the Environment Agency and English Nature publish comprehensive advice on what to and what not to plant, so it might be worth contacting your local office. Some good native species include Hydroctyle vulgaris, (Marsh Pennywort), Hydrocharis morsus-ranae (Frogbit) and Ranunculus aquatilis (Water Crowfoot).