Introduced coypu (Myocastor coypus) damage crops and natural vegetation and undermine riverbanks. We controlled coypu with cage traps to protect vegetation in 3 wetlands in the Park of the Rivers Po and Orba (northwestern Italy). During a 3-year trial, coypu were controlled in the Natural Reserve of Valenza (NRV), an area with a low degree of colonization, but not in one with a high immigration rate. In NRV park wardens were involved for 18 man-days of work annually, and the cost was 1,518 Euros (1,867 U.S. dollars) per year. From 2001 a control program was carried on in the 3 areas. Removal densities (0.06–1.3 animal/ha) suggested that 2 trapping periods annually were adequate to slow down coypu population increase. The recovery of yellow waterlily (Nuphar lutea) in 3 plots and colonization of new ponds by vegetation indicated that coypu were maintained at a level sustainable for vegetation development.