A drop in the bucket
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If a drop of rain fell anywhere in the US you choose, what path would it take to the ocean? River Runner will show you and it does it with a really awesome 3D view. Try it out here:
https://river-runner.samlearner.com/
The javascript source lives here and uses USGS NHDPlus data and their NLDI API to visualize the path of a rain droplet from any point in the contiguous United States to its end point (usually the ocean, sometimes the Great Lakes, Canada/Mexico, or another inland water feature). It’ll find the closest river/stream flowline coordinate to a click/search and then animate along that flowline’s downstream path.