Click on the map and find the watershed/drainage are for that spot. List all tributaries (you can sort them by length etc) allows for upstream/downstream navigation. Also shows the way the water takes to the sea. Search by address or river name as well. Overlay additional resources like snow, reservoirs, water diversions, watershed importance to drinking water supply etc. It’s possible to embed in websites, share via URL and use on a mobile device in the field.
Full instructions here:
Santa Cruz River above Tucson: