Pond Boss Forums GENERAL QUESTIONS Water chemistry Bottom of the pond water

My pond has been running full for several weeks with frequent small flows thru the overflow pipe that draws off the top. Downstream of the dam I have 4 small settling pools. They drop out any sediments (mostly non-pond runoffs) and sometimes dry out between rains. When fed normal surface water, the pools take on a green hue and sometimes get a thin green scum when slow/stagnant.

This weekend, pond was full and more rain coming so I opened the drain line. It draws from 8-15' down. One can posit that it's under the thermocline- it's cool. Running the drain, overflow stopped. After a day the settling pools had all black water. It developed an orange foam downstream of the first rocky drop where oxygen might be added. After I closed the drain, the first pool had a shiny film on it that looked almost like oil. There is a distinct unpleasant odor, perhaps a sulfide? I was in the creek and the dark water and odor was observed quite a way downstream from where the branch dumps into the creek.

Is this typical anoxic water? For now I only have forage fish, but seeing all that doesn't breed confidence that large fish would want to be there in the future.

Your asessment was right on the mark.

The orange is un-oxidized iron becoming oxidized and no longer soluble so it precipitates out as rust. The oily sheen is organics breaking down, and the stink is sulfides.

Our local retired reservoir has the bottom drain running in one of the two 20+ acre ponds to drain it down, and the stink is horrific. Enough to gag a maggot. Even the dog was not pleased, which when it comes to stink, she typically loves it. The water comes out a milky black, and rust deposits along the outflow downstream.

Makes a person want a bottom draw overflow system, doesn't it? Or at least aeration to keep it from becoming anoxic.

If anyone is interested, I took photos & can add.

Thanks for the details on what the observed features really were.
Water coming out the pipe is clear; then it hits the pool. And the dog didn't seem to mind, though I did get a chuckle when it tried to jump the deepest spot and failed. This weekend I had the cairn with me. Very short legs, but happy to try anything- including swimming out to sample some feed.

Bingo Snrub. Piping is what it is, though I am fortunate to have a drain to play with. Aeration can be done with some work. Just have to decide if next year when 2-3" predators go in, or can it wait to the next year when they'll get more size.