apparently, the dumping of used oil, antifreeze, paints, and other awful (household) chemicals are the primary source of pollution of the charles river. so.... most stormdrains have a sign like the one above, reminding people not to just carelessly dump their sh*t, as it will go straight to the charles river etc...
this one is actually on the bridge that i showed you yesterday.
as a kid, i sometimes used to make "soup" in such drains. we would throw in sand, mud, leaves, anything we could find and then stir it with a large stick... i guess that was one of the reasons they sometimes got clogged and all the rainwater accumulated at the little "playground" behind our house.... ooopss!