Streamer

The national atlas has a cool tool, called streamer which allows to trace rivers. Try it out. Here are some upstream tracers. The tool shows interesting things: how river upstream patterns become fractal, where watersheads appear. The middlesex channel for example crossed over from the Mystic river to the Merrimack river.

Charles river

Merrimack river

Concord river

Mystic river

Connecticut river

Hudson river