Rotenone
"Water
Rotenone is highly toxic to fish: most values for the 96 hour LC50 (lethal concentration required to kill half the test organisms) for different fish species and for daphnids (water fleas) lie in the range of 0.02 to 0.2 mg/litre. If used as a piscicide, it may also cause a temporary decrease in numbers of other aquatic organisms.
There is considerable controversy over the use of rotenone to kill non-game fish in water body management areas. One study found that the practice has a substantially harmful effect on biodiversity, in which several populations of the native fish showed negligible signs of recovering stocks, while populations of all exotic species are up."
Not ridiculing anyone, but using poison will decimate everything in that watershed, it will not specifically work only on carp. Carp is a hearty fish, a true suvivor.
After talking about this with my dad today, he figures he caught about a dozen of different year classes of prussian carp from same location within a year. They've been around for more than a decade in Alberta that's for sure. They are now a part of the ecosystem. Sad to see, someone wasn't careful with their fishpond and forgot to warn authorities when things went wrong.