Pond Boss Forums Thread Like Summary - Bass Dying all of a sudden

My 1 3/4 ac pond seemed to be doing well but over the last several weeks I've found 4 mature dead bass floating - found a couple large ones maybe three weeks ago floating -- both in ther 4lb range and today I found a couple more in the 2lb range.

I had a good bloom going from late may to the end of July 18" to 2.5' visibility. The water cleared up around beginning of August and it was shortly after that I started seeing floaters.

I'm leaning toward killing off all the remaining watershield in the pond as I think that is what killed the bloom. I'm thinking maybe the bass were having trouble feeding in the clear water (noticed the last bass I caught looked skinny) and/or the O2 levels dropped.

We did have some big rain storms but I don't think the pond turned over as I didn't see any dead BG - normally when I get some turn over I see a few dead BG - never had an issue seeing dead bass before.

FishinRod Has posted a very good & very likely senario.

About 25+ years ago our 3 acre retention pond was full of weeds & we had a week of hot 90s, overcast, with very little wind type weather. We lost about 20 LMB & 20 grass carp all in the 2-3 lb & above range. The smaller fish seemed to tolerate the low O2. Called the local fish farm for advice & he said other ponds in the area had the same problem. I really do not think it is a lack of food problem. Lack of food would be a weeks or months problem to kill the fish. I now have a long term, 20 yrs, over population of LMB. Rws of 75 & below, they are not exactly health but they have adapted & survive.

Doing RWs of your LMB is the key to telling you if your LMB are getting enough to eat. If the Rws are low then there is probably to many LMB in the pond for the amount of forage fish.

That watershed is part of your ponds natural ecology. The fact that it consumes some of the nutrients is a balancing & stabilizing factor. With no littoral zone plants & all the nutrients available for the algae you may have tremendous boom-and-bust cycles & frequent times of extreme low O2 with large fish dying. One of the fish farms has a very good article as part of their web site about how the cycles develop.

https://americansportfish.com/fertile-ponds-and-plankton-blooms/

The littoral zone is where the forage fish survive, hide, & grow. Where they get a chance to become 2-4" fish. Your 2-4lb LMB are thankful. The lack of a well developed littoral zone is one of my problems. The fry & fingerlings get eaten well before they get a chance to become good forage fish.

The pond is a balancing system: A change here will always produce a change somewhere else.

Just a thought, and ez to check out. This spring I found a newly deceased walleye , 23" long , still very flexible and decent coloring.
Opened up stomach , back half of a plastic creature bait in stomach and stuck into exit to intestines. it was very skinny. I've had back 1/4 to 1/2 of plastics bit off my self on occasion, clients tell me of this happening to them , and no doubt that fishermen , not thinking of consequences , throwing badly damaged plastics in water , rather than taking home to garbage. Once in the currents of the BOW, they appear as food. Just a thought , if these fish are skinny , might double check stomachs , especially if a lot a plastics used in your BOW.

esshup delivers fish to customers. He has a very nice (expensive) DO meter.

I think you can find a discussion of various meters if you search the old threads.

"O2 levels are lower or at least the water has the ability to hold less of it as the water is the warmest in the summer."

You got it! The warmer the water the less O2 for the fish, even without a vegetation kill.

Much safer in the cool months. Chemicals most effective when plants are putting energy down in the roots to over winter & next springs growth (Fall).

You can play it safe by doing your pond in stages, so that everything is not all decomposing & using up O2 at the same time. Perhaps doing just some areas & leaving others natural & see if you have the desired effect your are looking for? 20% is often mentioned as a minimum goal for the surface area of a pond to be covered with weeds. An area for biodiversity of the pond.

My bet is that the herbicide spray combined with no aeration and high water temps created an O2 crash, and without aeration it is taking the pond a long time to recover. I saw it in a friends pond that I have been after him to get aeration in for the past 6-7 years. It finally bit him in the butt. 3' TGC, 20+" HSB, 4#-5# LMB and 8"-10" BG dead 3-10+ days after spraying about 1/4 of the pond for coontail/algae. He has been guessing at water temp too, and finally broke out the thermometer to actually check water temps.

I checked the O2, and in the afternoon when the O2 typically is highest, he had 5-6 mg/l, but go down 3 feet and it was in the 4mg/l range and below 4 feet it dropped to the 3mg/l range. 6 foot was below 1 mg/l. Surface water temp was in the low 80's. He first noticed the fish stop feeding, then a few days later started seeing dead fish. The O2 would vary according to water temp, and a suppressed feeding response was a good indicator of dangerously low O2 levels.

We threw in a bottom diffusion aeration system with 2 single disc diffusers with a 1/4 hp compressor in the pond, but that still isn't enough for a 2 ac pond with a max depth of 12'. A larger compressor can't be used, the power supply can't support it. We tried with a 1/4 hp and 3/4 hp rotary vane compressor and the air output was less than with the 1/4 hp rocking piston compressor. That will be changed for next year, and a 3/4 hp rotary vane compressor will be used with 2 more airstations.

It took 3-4 weeks for the O2 in the pond to come back up to where the fish are feeding now, and in part I think that is due to cooler water temps (by 5-6 degrees).

Multiple fish don't die at the same time from starvation or low food availability - it was an O2 crash. The herbicide used had no effect on the fish kill other than killing the plants that then decomposed and the bacteria that was decomposing the plants sucked up the O2 which in turn caused the fish kill.