Chicago River zooplankton taxa abundances which exhibited significant differences before and after a large CSO event based on samples from three locations in 2023. Three locations were sampled, with the disturbed location received 9.1 billion litres of untreated effluent over two weeks. Shared letters indicate statistical similarity among locations within each period (‘a/b’ before CSO, ‘x/y’ after CSO), while asterisks denote changes within locations before and after the event.