As part of a more than fifty-year-old Chicago tradition, the Chicago River is dyed green in observance of St. Patrick's Day.
The tradition of dyeing the river green arose by accident when some plumbers used fluorescein dye to trace sources of illegal pollution discharges.
The parade committee has since switched to a mix of forty pounds of powdered vegetable dye.
The dyeing of the river is still sponsored by the local plumbers union. The dye takes days to dissipate.
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| Here you can see where the dye was first added to the river |
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| Speed boats run up and down the river to mix the dye |
