Yearly mean fish assemblage anomalies (similarity to the grand mean assemblage) and their cumulative sum (CUSUM) over 35 years in the Chicago Area Waterway System, calculated using abundance (grey) and biomass (black) data identify the late 1980s and late 1990's as periods of rapid change. Lines represent significant piecewise regressions (minimum of 3-yr spans; α = 0.05). Different shapes represent groups with significantly different means (α = 0.05) within each index.