We started off with perhaps two tablespoons of duckweed that were sourced from local ponds. We used chicken poop that we had purchased from a local man who bought it from a factory farm. The smell only occurred when we were mixing it in a trash can to add to our ponds. The ponds never smelled of manure or stagnant.
The waste I was referring to was the runoff from some farms. Cattle, pigs, chickens all produce a lot of waste. The use of duckweed can help minimize the effect of such waste. As I said, we only used chicken manure that we purchased.