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.

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

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

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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.

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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.

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