Anaerobic breakdown of organic debris causes most of the odor you
describe. Aeration should solve the problem. Get air to the deepest
parts of the pond to ensure circulation of oxygenated water at the
bottom, where the source of the stench exists. Your waterfall is not
doing this for you.

"Jackytar" wrote:

My wife and I notice a sewer smell when we get close to the water in our
fish pond... as in bend over with our noses just over the water or when we
get in there and stir things up. The plants and fish seem healthy, and the
water is clear, although we found one dead fish today (out of about 20). The
pond is about 1000 gallons (my estimate) and 3 yrs old with a
skimmer/pump/filter/auto filler set up. I must admit we haven't been adding
the "aquaclear" bacteria powder or cleaning the filter very often (about
once every 2 weeks). We have an overabundance of water hyacinth right now
that we are thinning out.

Thanks,
Jacky