The paradox dissolves once the unit of assessment is clear. The Red List evaluates wild Cyprinus carpio in its native range across parts of Eurasia, where genetically distinct populations have declined through habitat loss, river regulation and hybridisation with introduced domesticated stock. Introduced and farmed carp elsewhere are not what is being assessed.
Outside that range the same species is a problem. Carp feed by rooting through soft sediment, which suspends silt, uproots aquatic plants and releases nutrients into the water column. In parts of Australia and North America this has shifted shallow lakes from clear, plant-dominated states to turbid, algae-dominated ones, and control programmes are long-running and expensive.
What is not settled is how much of the remaining native genetic diversity survives uncontaminated by escaped domestic strains, since introgression can be invisible without genetic sampling and few wild populations have been surveyed in depth.