Step 1 : Introduction to the question "What U.S. city dyes its river bright green each year for St. Patrick’s Day?"
...Each year since 1962, the city of Chicago has celebrated St. Patrick’s Day by dyeing the Chicago River a vivid shade of green. The tradition began when local plumbers used a special vegetable-based dye to trace pollution in the river and discovered it produced a brilliant emerald color. Today, the dyeing of the Chicago River has become one of the city’s most famous holiday traditions, drawing thousands of spectators and tourists each year and kicking off Chicago’s large St. Patrick’s Day parade and weekend-long celebrations.
