I artificially started my siphon today on my two year old 5 acre pond in order to do some work around the shoreline. It has ran several times naturally over the last two years. It has been running for about two hours as of now and has been spewing out thousands of gallons of murky dark nasty looking water that flat out stinks. It is emitting that dirty/mud/sewer type smell. I have watched it run in the past and not noticed the smell or the dark water, but that was always after a substantial rain. It ran on its own about two weeks ago and the intake is about 8' deep and 5' off the bottom. The pond water is by no means clear at the top as it has about 16" of visibility due to clay/dirt particles. Is the nasty water/sewer smell normal? I know its supposed to get rid of the nasty water on the bottom of the pond but dang I didn't know the water down there was this nasty...?

Anaerobic bacteria smell really bad. Unless your pond is aerated, after you siphon off this layer it will just restratify and make more.

I'm guessing that you don't have a bottom diffuser aeration system in the pond. That's exactly why those systems are recommended for ponds - to eliminate that type of water.

That's normal for a pond that doesn't have one. Maybe not the black color, but the smell, yes.

Correct, I do not have any type of aerator/diffuser in the pond as I still don't have electricity there, but after seeing and smelling what I did today as soon as I get power out there I'm gonna seriously be looking into a system if it will prevent that kind of water from being in my pond. Thanks

Even if you have power a long distance away from the pond, and can trench in a buried air line you can get air to the pond. You can push air a long distance for far less $$ spent than it costs to bury electric.

Just remember not to crank it up full blast right away during the summer or you will be bringing up all that anerobic water and potentially causing a fish kill.

Here may be the answer. If you turn on the siphon in summer after the lake has formed a thermocline then the deep water will most likely smell. If you do it in winter spring and late fall after turnover (or when lots of rain) then the deep water has O2 and less sulfur smell.

Eric,

Why would he want to siphon off the water when it is no longer anoxic? What am I missing here? Or did you mean turn on the compressor at those times?

Sorry not something I'm used to dealing with as I use diffusers to break up the water columns in my ponds. And my ponds are not very deep.

As he stated to draw down the water level to work on the pond.

The question is about the water smell (H2S) and not why to turn on the siphon.

Got it. Missed the part about drawing down.

Could it also have something to do with it not raining, no matter what time of year?

My thought is that when it rains heavy enough to be used, could that water be mixing with that bottom layer and making it less noticeably smelly.

It might need a LOT of rain to do that. I had enough rain to raise my pond (increase it's depth) by about 25% (pond rose about 36"). The thermocline went from 8' down to 14' feet, and there still was a couple of feet of water under that thermocline to the bottom of the pond.

Yes that could happen also. Rain water is colder than the pond in summer. As it goes in if enough volume because it is colder it will sink and effect the thermocline. Problem is that can lead to a turnover and fish kill.