Traditions of St.Patrick's Day:Green in 30 seconds:

          Amazing timelapse of how Chicago River is turned emerald for St Patrick's Day

The Chicago River has been turned green in honour of St Patrick's Day for more than 50 years. Tradition started from the city's efforts to detect illegal sewage dumping. Plumbers put fluorescein dye in the river which turned bright green if toxic sludge was detected

Now a harmless orange vegetable dye is used to get the desired green hue

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