watermilfoil, a plant that invades canals and threatens biodiversity

They proliferate and gradually suffocate the Somme Canal. Watermilfoil is a plant that clings to boat propellers and even to fishermen’s hooks. Every year, the Department must finance a weeding, the equivalent of a mower passed to the bottom of the waters. The problem is treated, but not really solved since the plant grows back. “We have not yet found a solution to eradicate the plant”, says Hubert de Jenlis, vice-president in charge of finance and operation of the Somme. 200 km away, in Honfleur (Calvados), we find this invasive plant in a pond.

Banned today, but long sold for aquariums or small ponds, they threaten ecosystems. “This plant is sold in garden centers for its oxygenating capacities (…) except that it is the opposite effect since, when it will have completely colonized the pond, there will be no more photosynthesis possible and therefore there will be a middle suffocation”, explains Rémi Mandra, from the Norman brigade “Invasive alien species”. The navigability of the canals is also impacted. Many rivers in northeastern France have been affected in just a few years. France’s Waterways Department invests 3 million euros each to tackle these plants.