Mulch causing die off in a pond?

[enrgizerbunny]

My boss recently had his entire pond die off and the only thing that changed was that he had accidentally blown some mulch into the pond while doing leaves. He's suspicious of a poisoning because the mulch had been outdoors for over a year and ALL the fish died in that pond. Had anyone had a similar experience? These weren't baby fish either, one of them was a 20 inch butterfly koi.

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[Delapool]

Ouch, nasty

 

[enrgizerbunny]

For clarification: He suspects someone else may have poisoned the pond, not the mulch.

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[Fresh2o]

I'm thinking this may be more of the case rather than the mulch. Either way, sorry to hear about this.


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[Brookster123]

Sinister..

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[henningc]

Some mulch has highly toxic fungicide and that may have done it.