I think your map is very interesting and looks nice. It has a very distinct style. Rather than lighten rivers perhaps the real issue is the choice of where to use black lines and where to make a coastline with blank water like your seas. I think what may be troubling to some is how the rivers get large at their mouths and why aren't they coasts or fjords at that point instead of black river lines. The same goes for the lakes, why black? Just a thought. I had a similar issue with the rivers in my Linlandia map. I re did them with a smaller ink nib size in GIMP and it worked out reasonably well. Just some thoughts.
I'd darken and/or fatten the coastlines to fit the rivers but I like it.
If the radiance of a thousand suns was to burst at once into the sky, that would be like the splendor of the Mighty One...I am become Death, the Shatterer of worlds.
-J. Robert Oppenheimer (father of the atom bomb) alluding to The Bhagavad Gita (Chapter 11, Verse 32)
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I think it's coming along very well. I love the mountains and the trees best of all. The mountains are very well done. I liked the mountains a little more when they were less dark, but when you darkened them it helped out the rivers a bit.
I like the dark rivers, and I think to offset it a the coast line just needs to be fattened up a tad, so to speak. Other than that, the trees and mountains are gorgeous, and I have to say, the little volcano was very amusing for some reason.