Why can't we do this to the Charles River?

In Chicago they dye the Chicago River GREEN
for St Patrick's Day. Why can't we do the same to the river Charles?

Causing skepticism in some and delight in others, the river has been dyed green every St. Patrick's Day since the early 1960s by a pipefitters union. Walk by it in broad daylight any other time of the year and the river is a dark green, prompting the famous line from the movie, "The Fugitive," "You'd think they could dye it blue the rest of the year."