Pond Boss Forums GENERAL QUESTIONS Help Fish kill - help

I arrived at my 3 acre pond the other day and noticed several floating white masses. Went out on my floating dock to discover there were 20-30 dead bass and a couple grass carp. It was only the largest of fish that died. I saw no small fish. Went out again today and didn’t notice any more, so I think it was a one or two day time that they all died in. I also saw the elusive white koi that has to be 20 lbs or so, that I’ve seen lurking the last few seasons, and it was alive and swimming.

We had a HUGE downpour a week before I noticed the kill, where my pond rose about 4 feet in one night. The water turned brownish, but has since gone back to its normal green color.

I have aerators running 24/7 that have been in for four years.

Any ideas on what I should look at to figure out what caused this? I’m four years into owning this pond and was really unhappy to see the largest of my bass floating around dead.

Thanks!

Common themes I've seen on questions for items like this are:

1. Any recent fertilizer or weed killing treatments before the rain?

2. Pond Size and Avg Depth? Might also be helpful to know if the pond was full / close to full before the rain or was all of the water captured retained.

3. Have any water quality testing before/after the fish kill on PH and Alkalinity?

4. Anything visibly different other than the stained water noted between the rain event and fish kill?

I would be guessing but if you are currently aerating a pond turn over on water temps probably it's part of the cause. This assumes that you are aerating most of the pond and it's adequately sized/functioning properly.

Sad news on the loss of the fish. Hang in there.

The massive inflow would be my first guess. A rapid roll of the pond with cool rain water can bring toxins up, mix and cause issues as well as rapid change stress. The big and the smallest seem to suffer-Visibly-the large often bloat and float (a percentage) and often the YOY sink, not to be seen.

Thank you both for the replies!

1.I have not fertilized or used any chemicals recently but it’s possible the neighboring farm did. I think a big part of the runoff came from a farm behind my pond. It’s been dry since I bought the place 5 years ago, but there is a clearly obvious place where water has flowed before that heads towards my pond.

2. 3 acres, 6ft avg depth. Yes all of the water was retained and the pond was about 6 feet lower than when I bought it. It rose about 4 feet in one night.

3. Water test before but not since. “Ultra pure” was what the test called it.

4. Some floating foam/scum is the only thing I have noticed. Water seems to be un-muddying too, going back to normal.

My aerator pump was just replaced so it’s working great. It might be slightly undersized. Have never had a fish kill before and it’s been a lot hotter in years past than so far this year.

Should I not run the aerator 24/7 when it’s hot? I was under the impression that once you get to 24/7 that it should stay that way forever. That’s how it’s been for 4 years.

Thanks again!

There are two schools of thought on aeration. 24/7 is used by some and evening hours are used by others. I'm no pro here but here's my understanding:

24/7 operation has a continual input and mixing of the water which is a good thing most of the time but there also might be some design criteria that is taken into account. The consideration is how frequent is the water turned over. In the extreme weather (hot or cold) running the system can heat or cool the water basically taking out the deep water refuge.

The guys that are running their systems only at night rely on plants, wind/wave action, and phytoplankton to provide O2 during the day and then in the evening kick the system on when there is no photosynthesis to keep the O2 input going. This helps to prevent the solar input of additional heat and hopefully keeps the deep water refuge a little cooler than the shallower areas. It might require a larger system to still turn the water over in a shorter timeframe.

Again, I am no pro. Hopefully somebody will chime in with additional info or to correct what I've stated if I've listed something incorrect.


4' of water over 3 acres is A LOT of water in a short amount of time. Very likely PH, Temp swings and possible toxins released with the inflow. We have beans planted this year on part of the watershed that feeds our pond and the farmer just recently sprayed the beans to kill off any weeds that were present in the crop. Not sure if you are in a similar boat with crops in the watershed but that might have been a contributing factor as well. 4' of water would likely be water inflow from 100% of your watershed.

I have confirmed (to the best of my ability) that the water did indeed largely come from a bean field watershed.

Many large bass and a couple of my (less than 7) remaining grass carp are dead. They have now all sunk or otherwise disappeared. I saw no small fish, but have seen the one elusive white koi that has been the only fish I can spot from the bank, still swimming.

I checked my feeder and it was gummed up. In fixing it I allowed about 15 lbs of feed to spill into the pond. I saw no activity around the floating food. It would normally have caused a frenzy of bluegill, so that scares me.

I initially theorized that only the largest fish died because that’s all I saw. The white koi is the largest fish I’ve seen ever in my pond. I am now thinking that only the largest fish survived. What do you all think? What’s more likely to die, the large or small, from a herbicide runoff situation?

The positive: My pond has suffered from turbidity issues all year. It got muddy looking after this big rain. It has now cleared even better than after I did an alum/lime treatment a few years ago. However I had zero bites while fishing for an hour, so that scares me even more that nearly everything died. I normally see turtles all over too, and saw none.

Good news is that is sounds like the pond is clearing up, the water is stabilizing, and you aren't seeing additional fish kills. I guess if I were in your shoes I would do the same thing on making sure the feeder was operating properly. Also sounds like you confirmed your aerator is working properly.

If you don't have the ability to test the water currently, I'd be for buying a swimming pool test kit that would at a minimum test for PH, Alkalinity and Hardness. Log your results for a couple of months for reference and decide at that point if you feel like you want to make a change or like what you are seeing. API sells a relatively inexpensive one and LaMotte sells a more expensive kit. I have both, and prefer LaMotte for the most part but either would help you to get some baseline info on the pond chemistry for a couple of bullet points.

What i see on our pond after a big rain event is that the water PH and Alkalinity fluctuate quite a bit and over the next week or so as the water gets mixed, we end up right back or very close to where we started. That initial boon of water does change our chemistry for a short period of time. The good news here is that you now have another 4' of water in the pond which should help to buffer the swings in PH by the next water event.

On the fish, I'm in a little different place than you are. We are in the first growing season of our spring stocking and my plan currently is to leave the fish alone as much as I can until we get to Sept 1 or the weather starts to cool for Fall. Our fall testing will likely include trying to trap some of the forage base in traps or cast nets. I will be looking to see how we did on recruitment specifically and whatever the results from that are either try to add to it or let it ride. I would guess that you didn't have a 100% fish kill of any species and given a little time the remaining fish population will respond to not only the additional water but any shortage trying to fill the gaps naturally. Typical stocking of the fish falls into this for Spring and Fall so for now....let it ride.

Good luck Curt. One of my biggest struggles is to not rush it. Some of this stuff just takes time.