My son and I like to walk 5 minutes down the road to fish a little pond. It's a great numbers pond. Occasional 3 and 4 pounders, but usually 1-2 pounds and less. Well, we walked down yesterday afternoon to see that the water had suddenly turned rancid, and we stopped counting at 43 dead bass, catfish, and bluegill, mostly because of the smell. It was all so sudden. We had just fished it a couple of days prior, and the fish appeared healthy and fine and the water, while weedy, was good looking. 

 

The town took action pretty quickly. A few hours later clean up crews were down there taking out the dead fish and weeds, and some kind of pump or filter was going.

 

What could have happened?

If you want an expert answer, go check with the guys at Pond Boss Forums.....I'll take a stab and say there was a turnover event that depleted all the oxygen and choked them out.  This can easily happen, but I think for turnover to occur, the water must be more than 9' deep.  Otherwise, weeds might have died and decaying caused loss of dissolved oxygen.  

 

There's also a lot of great articles on this site (many of which come from contributors at Pond Boss) under Fish & Lake Management that could help pinpoint an answer.  

Algae bloom? 

 

Are there a lot of residential areas where runoff flows into the pond?

What does the town say. If they have a pump going I would hope they know what their pumping.

I actually just talked to one of the guys working on it. The plant life died and sucked the oxygen out. They went in cleaned it out, have an aeration system, and got with the DNR and will be restocking it when it's ready.

 

So the answer is, it turned.