I am trying to figure out if there is a way to calculate area on a line (river) between two points (dam) for an entire watershed. In a way I want to make a corridor of where fish are able to move freely between dams. Any suggestions are appreciated!

[KatelynVardy]

I am trying to figure out if there is a way to calculate area on a line (river) between two points (dam) for an entire watershed. In a way I want to make a corridor of where fish are able to move freely between dams. Any suggestions are appreciated!

[JoeBorgione]

By definition, a line only has length.  Using linear geometry to model rivers, streams, and canals is a common practice but clearly has it's limitations. If the data exists, you could model your streams using a linear reference system approach where reaches are given a width. Very data intensive.  You could also buffer the lines with some sort of average width and find area that way. Just to toss another challenge at you, shouldn't channel depth and or morphometry  be considered as well?

[DuncanHornby]

RivEX for ArcGIS Pro has the Link Sites tool designed to create the polyline linking two points on a river network. This tool will generate links between all combinations of points.

If you want to understand the network between dams and thus the entire available network for the fish rather than a single route then RivEX has Create subnetworks tool.

In fact RivEX has many other tools designed to pull out geometries aligned to the river network which can then feed into further analysis or visualisation.