Vegetables are healthy and cheaply available in Germany, which is great news for consumers but less so for Europe’s largest saltwater lagoon. Once, local youngsters swam in its clear waters. Now, no one goes near the dark brown sludge that is packed with dead jellyfish, the waters ruined by agricultural runoff. Intensive farming activities nearby are killing the lake and all that lives in it. Activists are demanding change from local businesses, regional officials and also supermarkets in countries like Germany. No one needs four harvests a year, a campaigner told dpa, in one of the newest gri…