Variables importance, as assessed by both the percent Increase of Mean Square Error and Increase in Node Purity, in the Random Forest Regression model; significant variables (permutation test) are shown by red bars (1. Discharge; 2. Water speed; 3. Water turbidity; 4. Mean width of the wet riverbed; 5. Mean width of the riverbed; 6. Mean river depth; 7. Pollution; 8. Mean riparian vegetation width; 9. Mean % cover of (semi-)natural vegetation; 10. Mean % cover of aquatic vegetation).