Resource agencies are searching for effective methods to prevent the spread of invasive Silver Carp (Hypophthalmichthys molitrix) and Bighead Carp (Hypophthalmichthys nobilis), hereafter bigheaded carps, from the Mississippi River basin into the Laurentian Great Lakes. Elevating carbon dioxide (CO2) concentrations in water within locks and other pinch points is an approach being considered to reduce invasive fish passage. Laboratory studies have shown that bigheaded carps strongly avoid areas of elevated CO2 (Kates et al. 2012; Dennis et al. 2015). Similarly, telemetry studies found that CO2 can be used to exclude bigheaded carps from certain locations (Donaldson et al. 2016) and reduce upstream movement (Cupp et al. 2016). Previous studies were completed under controlled settings, and research to determine the feasibility and efficacy of elevated CO2 to control bigheaded carp movements in larger natural environments is needed. On October 21–28, 2016, the U.S. Geological Survey Upper Midwest Environmental Sciences Center, Illinois-Iowa Water Science Center, and Columbia Environmental Research Center conducted a short field study at Emiquon Preserve (15T 750386.95m E, 4469041.70m N) near Havana, IL. Objectives for this study were to (1) characterize CO2 concentrations and distribution at various water velocities and (2) determine the effectiveness of CO2 to reduce general fish abundance and movement. During this study, water quality, atmospheric CO2, and fish presence were quantified across three water velocities (no flow, restricted flow, and unrestricted flow) with and without CO2 injection. The study was conducted at the water management structures (WMS) which served at the single connection between an isolated backwater lake and the Illinois River. Carbon dioxide was injected into the downstream portion of the WMS using air diffusers connected to compressed CO2 tanks. Fish abundance and movement was quantified using two Adaptive Resolution Imaging Sonar (ARIS) transducers placed across WMS entrances. Water quality was quantified using stationary sondes, grab sample, and mobile transects. Atmospheric CO2 concentrations were quantified at fixed locations throughout the study site. Dates and times of importance: no water flow with CO2 start (21OCT2016 0800 CDT) and stop (21OCT2016 1600 CDT), modified flow with CO2 start (25OCT2016 0800 CDT) and stop (25OCT2016 1600 CDT), unrestricted flow with CO2 start (24OCT2016 0800 CDT) and stop (24OCT2016 1600 CDT), no flow control day without CO2 (28OCT2016), modified flow control day without CO2 (27OCT2016), and unrestricted flow control day without CO2 (23OCT2016).