Planned sample sites for designed bioactive organic contaminants (BOC), including pharmaceuticals, have been detected in surface waters at GRSM , raising concerns for sub-lethal effects and potential apical impacts, including reproductive success, in sensitive aquatic populations in the park. GRSM is within a day’s drive of more than half of the U.S. population and has the highest visitation (more than 11 million annually) of any of the National Parks, amplifying the risk of visitation-driven BOC impacts. Of particular concern is the potential for adverse impacts of pharmaceuticals and pesticides released to park surface waters (including streams with threatened species or species of state concern) in the effluent from multiple wastewater handling and treatment facilities within the park. Because of high visitation, the impacts of pharmaceuticals and other BOC in individual waste releases are also substantial concerns for aquatic biota in numerous streams connected by the many high-use trails at GRSM. Moreover, although surface waters originate (headwater) within Park boundaries, greatly reducing or eliminating the risk of fluvial BOC transport into GRSM from external sources, the high elevation, central ridge promotes wet and dry deposition of atmospheric contaminants particularly along the western slope, raising the concern of atmospheric delivery of biocide (pesticide) contaminants to remote streams, as described previously in high elevation park ecosystems. Limited reconnaissance water sampling conducted gratis by the USGS Environmental Health Mission, Drinking Water and Wastewater Infrastructure Project in December 2014 documented the presence of pharmaceuticals and endocrine-active wastewater indicator compounds in surface water downstream of multiple visitor centers and campgrounds in the park.