In the Chesapeake Bay region in Maryland, where they were introduced in the 1940s, coypus are believed to have destroyed 7,000 to 8,000 acres (2,800 to 3,200 ha) of marshland in the Blackwater National Wildlife Refuge.
Na rexión da baía de Chesapeake en Maryland, onde foran introducidos na década de 1940, estimábase que o coipú destruíra de 2.800 a 3.200 ha de marismas no Blackwater National Wildlife Refuge.