Thanks to the USGS, an interactive map that lets you trace streams and rivers to their outlets. Click on a blue line and trace it upstream or down. Impressive.
Try clicking on the Chicago River and take a look at the long, improbable red line going all the way down the Mississippi, instead of quickly dumping into Lake Michigan. For those of you who don’t know the story, check out 99% Invisible’s feature. And subscribe to their podcast if you haven’t already.