Came upon this h/t  Trout Underground re Carp in Malheur Lake: “Carp are native to Europe and Asia and were artificially introduced into the Silvies River in about 1920, probably to keep nearby irrigation canals open on the premise that carp would eat aquatic plants and algae, Beck said.

Their numbers in Malheur Lake — which averages 18 inches deep — verges on the unbelievable. Biologists estimate 1.5 million carp inhabit the lake….”

WOW!

Historic data of Rotenone treatments of carp at the Malheur National Wildlife Refuge:
1957: 1.5 million carp killed in Malheur Lake and nearby Boca Lakes
1959: 58,000 carp killed in Blitzen River and Sodhouse Pond
1960: 400,000 carp killed in Malheur Lake and Blitzen River
1961: 150,000 carp killed in Malheur Lake and Blitzen River
1968: 240,000 carp killed throughout refuge
1969: Blitzen River treated with rotenone, number of carp killed unknown
1977: Unknown thousands killed in Malheur Lake and 50,000 killed in Blitzen River
1992: 100,000 killed in Blitzen River and Sodhouse Pond