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Removing weeds from Dal Lake, Srinagar, Kashmir, Jammu and Kashmir State, India. The weeds are created by  raw sewage flowing into the lake, which creates an unhealthy influx of nutrients, mostly nitrogen and phosphorus, acts as a super-fertilizer. The result is an explosive growth of duckweed, water ferns, and algae that eventually depletes the water of the oxygen vital to fish and other aquatic life. Add to this a drainage system constantly clogged with muck, along with little wind to aerate the water, and the result, researchers say, is a lake in peril.