Where does the rain go?

Real waterways. A simplified journey. The map shows USGS National Map rivers, lakes, terrain and places. A click is assigned to a USGS NHDPlusV2 catchment, then the Network Linked Data Index follows its main downstream branch. This medium-resolution network omits some small streams and urban drainage. It is not a map of current flooding, water quality or live river conditions.

The first segment joins your click to an approximate point on the catchment’s flowline. It is not a terrain or storm-sewer simulation. The river segment follows mapped network geometry, including artificial centerlines through lakes and estuaries. Tides, diversions, groundwater, dams, infiltration and evaporation can change an actual drop’s journey. Animation speed does not represent travel time.

Routes stop where the available network stops, at a gap, or at the 6,000 km query limit. An endpoint does not necessarily mean the ocean. Coverage is for exploration of the contiguous U.S.; Alaska, Hawaii and other countries are not supported for new rain locations.

When a connected river trace reaches a verified Great Lakes shoreline, a schematic lake overview continues from its receiving lake through the downstream lakes and rivers to the St. Lawrence and the Atlantic. USGS lake outlines help the overview go around major peninsulas, including Door County. These approximate connections are not measured lake currents or travel-time predictions, and are excluded from the mapped-distance figure. If the shoreline connection cannot be verified, the display stops at the available river trace.

Four example traces were downloaded on October 28, 2026 and are served with this page. Other clicks request USGS data through Uncle Simple and cache the result. If that connection fails, your browser tries the public USGS service directly. The map requests only visible tiles from the USGS National Map. These services receive network requests. The map opens to the contiguous U.S. “Use my location” optionally asks your browser for permission and centers the map; a rainfall lookup happens only when you tap. This widget does not store your location. Tracing coverage is checked against generalized U.S. boundaries from Natural Earth public-domain data.