In 2008 The 3 Rivers Clean Up brought together volunteers in an intense three weeks aimed at revitalising River Pool, Quaggy and Ravensbourne rivers in Lewisham, Greenwich and Bromley.
Alongside litter, specific plants were targets, in particular Himalayan Balsam. With head-high magnificent pink blooms in July and August, its clear why it was introduced to the UK as an ornamental plant. Unfortunately in the absence of pests and diseases, and growing from seed to six foot faster than most other riverside plants, it out-competes other plants. When it dies down in autumn, riverbanks are left without the protection of perennial plant roots to hold them together through peak river flow. Himalayan Balsam is an easy plant to remove. However, to reduce its dominance it must be pulled up before its seeds are ripe because it only takes a slight touch to send seeds flying up to seven metres away. Removing Himalayan Balsam before it sets seed, repeated over many years, has been successful in reducing its dominance and bringing back diversity to the riverside flora of The 3 Rivers.