Pond Boss Forums GENERAL QUESTIONS Help Fish Kill

Our healthy 10 acre runoff fed pond shrunk to 1 acre through last years drought but we had good survival on BG, LMB, and CC as well as some 30 lb grass carp.
While the pond was low, we brought in a track hoe, rebuilt the dam and dug out some silted-in edges to about 5 ft to eliminate some cattails.
March and early April brought rain that partially filled about 5 acres. The fish were doing fine, BG & CC feeding at the feeder and catching good LMB. Late April brought more rain that filled the entire pond. Soon after, BG and LMB started dying. Now the grass carp and CC have started dying. I see no sign of any moving fish in the pond. No surfacing, no feeding at the feeder, no fathead minnow activity. My fish finder shows a few hits now and then, but not like normal. Something bad is happening in my pond.
Yesterday, there was a brown-green scum over about 10% of the pond with thousands of dead mosquito larvae in the scum. No chemicals nearby. The game warden came and took oxygen and ph level - checks OK.
This is extreme red dirt (NW Oklahoma) with lots of blue gypsum in the silt. Could there be a chemical reaction in the freshly dug out areas of the pond?
Any ideas?

Welcome to the forum, it's a shame that what happened is the reason that you're here.

I'm shooting in the dark here, fut hopefully someone can help. First off, I'd search for a contact at Texas A&M University to send a water sample to for testing. That might help narrow down the problem.

Did the fish start dying when the water started covering the new excavated area?

When you say runoff pond, I'm assuming that the pond is filled with surface run-off. What area does the water flow over/from before it enters your pond? Could it have come from a field that was sprayed for farming? (Insectacide or herbacides) I know you said no chemicals nearby, but I had to ask.....

What is/was the water clarity? What was the O2 and pH readings that he took, at what depth, what time of day were they taken, and how soon after the kill?

Thanks for your reply. I have taken a water sample and will be looking for a place to send it.

The water covered the newly excavated areas in early March. The fish seemed healthy and active and I didn't start finding dead fish until the pond completely filled in Mid April.

This pond is filled by surface runoff. The entire watershed is on our property and consists of native grass pasture land and some open areas of red clay/shale. We do not spray any of the watershed because the native grasses are thick enough that weeds are not a problem.

Water clarity is a problem after heavy rains because of the red soil. Usually the pond is very clear except right after a rain. The water has been tea colored during this fish kill. It is unusual for the water to be this color. The submerged water vegetation is unusually brown rather than its normal bright green.

I don't know the actual O2 and pH readings, but do know they were in the green part of the scale on the game rangers gauges and he commented that both were acceptable. We took the readings mid afternoon at about 6 ft. depth one day after the largest numbers of fish died.

I have sent in water for a test.
After doing much research on the problem, I'm leaning toward hydrogen sulfide. My neighbors at Langston University in Oklahoma have an awesome website with much information. http://www.luresext.edu/aquaculture/new%20pond%20management.htm

Let us know what the water samples reveal.

Please do let us know. I would be interested in knowing how the metal levels came out of the water test.

Dissolved oxygen is usually at it's lowest point right before sunrise, by mid afternoon O2 levels could have rebounded to an acceptable level. How much aquatic vegetation is in the pond? Did the water clarity levels drop enough after the rain to start a large scale vegetation and/or algae die off? That would be my guess.

Here is the water test info:

pH 8.1
EC 2790
Sodium ppm 337
Calcium ppm 223
Magnesium ppm 54
Potassium ppm 10

Nitrate-N ppm <1
Chloride ppm 321
Sulfate ppm 964
Boron ppm .096
Bicarbonate ppm 112

Total Soluble Salts TSS in ppm 2020.9
Sodium Adsorption Ratio 5.2
Potassium Adsorption Ratio 0.1

Sodium Percentage 48.5%
Hardness ppm 779
Alkalinity ppm as CaCO3 91.8