The following link takes you to a GIS based website where you just click a theoretical drop of rain at any point in the US and it will draw to route of your raindrop to its theoretical terminus.
https://river-runner.samlearner.com/?fbclid=IwAR2PIoO0C5af9oGbWe1bebTm-ngCG2-q0Ipes31cjCpKH_Avn6qxehrkVWQ