Intersex and other reproductive disruption of fish in wastewater effluent dominated Colorado streams

Intersex white suckers (Catostomus commersoni) were collected in Boulder Creek and the South Platte River downstream of wastewater treatment plant (WWTP) effluent but not at reference sites. Eighty-three percent of the 60 white suckers collected downstream of the Boulder WWTP in spring and fall were female compared to 45% upstream (n = 33). Only female (n = 16) and intersex white suckers (n = 4) were collected in the South Platte River downstream of the Denver WWTP in the spring. Gonad deformities and delayed follicular maturation were noted in some white suckers in Boulder Creek and the South Platte River downstream of the WWTP effluents. Asynchronous ovarian development was found in some female white suckers downstream of the WWTP effluents, but not upstream. The types and extent of sexual disruption differed in each river studied.