The expansion of the bed of the river Tarn in the city and the creation of a raw discharge linked to its expansion has slowed and lowered the level of the river that now sees the proliferation of aquatic buttercup which is reveling in the stagnant water. This has also led to a decline in wild populations of brown trout in this sector. Also waterproofing concrete and paving large areas has increased significantly water from rain discharged directly to the river inducing a phenomenon called "flush" that is quite destructive to aquatic fauna and the banks.