This tutorial assumes basic familiarity with Inkscape including the Bezier and Edit Paths tools.

First, Ctrl+Shift+D to bring up the Document Properties. Select "Snap", and make sure Nodes are snapping to Nodes.

1.png

Now select the Bezier Tool and draw the rough path of your river as a sequence of straight segments roughly the same length.

2.png

Next add major tributaries the same way. Start at the corners of existing paths. The line will snap to the corner automatically.

3.png

Select the paths and choose Effects → Modify Path → Fractalize. Turn on Live Preview, set subdivisions to 1, and pick a smoothness that look good. Apply when you are done.

4.png

Use the bezier tool to add lesser tributaries using the new segment length. Make adjustments to the paths with the Edit Paths tool as you see fit.

5.png