Hello rcn11thacr and welcome to Pond Boss. Sorry to hear it's bad news that brought you here. Hang on and one of the experts will be along to talk with you.

You mention "water oak tree limbs" I'm not sure what you mean by that. In certain circumstances oak can release tannins that I believe can be toxic to fish. But that may have absolutely nothing to do with what happened.

There are also types of algae blooms that can be toxic to fish as well.

But as I said hang on for an expert opinion.

JHAP
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"My mind is a raging torrent, flooded with rivulets of thought cascading into a waterfall of creative alternatives."
...Hedley Lamarr (that's Hedley not Hedy)