A stacked area chart shows the average body length of three fish species—Tuna, Trout, and Salmon—across grouped data indices, with each species rendered as a colored region using d3.stack and d3.area. The chart loads a CSV dataset via d3.csv, bins entries into groups of ten, and computes mean body lengths per species. SVG paths fill the areas with an ordinal color scale, while axes, labels, and a legend clarify the visualization. Interactive tooltips appear on mouseover, displaying the species and its average length.