Just a quote from the Newsgroups regarding the active ingredient in
Wasp spray and fish toxicity. By the way, the goldfish has survived
over 6 hours in the pond, well past the normal "death time" of two
hours, so I believe the residual wasp spray is the culprit.
Interestingly the poster quoted below says the active ingredient does
not persist in the environment very long.

Almost nothing more toxic to fish than pyrethroids, the type of poison
in wasp spray. Some pyrethroids are so toxic to
fish that the amount needed to kill the fish cannot be measured in the
water (part per trillion).

Check the label, if it says something like "resmethrin, permethrin,
tetramethrin, or any other -methrin", keep it far away
from the fish pond.

We spray wasps out in the lake with soap. Doesn't work very fast, but
it works.

For koi ponds, something like malathion or Dylox will kill the wasps,
but also not quickly. Those are not very toxic to
fish. Even rotenone (commonly used to kill fish) is not very toxic to
fish, takes a lot to kill them.

You might try orthene, smells bad, but not very toxic to fish, also
not fast at killing wasps.

Pyrethroids work very fast, are not very toxic to mammals, do not
persist in the environment, and are fairly "safe" as such
things go, just not for fish.