Our outfit visited the river 4-8 April - exploring the water between viools and Aussenkehr. What was immediately apparent to all of us is the health of the river here being a lot better than below aussenkehr (" the grape farms"). There is a lot of insect life under the rocks and you don't see the grey/white muck on the rocks. I would like to know what the f happens in that intensive grapefarm section causing the water to deteriorate like that?