Caught.

That's a good point. I did the rivers differently from the rest of the map. I created the shape of the rivers using the ink pen with a large size to get the overall shape. I then selected all rivers, shrank the selection a little and then stroked it with a 2.5 pixel line. That's the reason for the solid black outline.

I don't mind them being wide for the map - the sizes are certainly not to scale - see the standing stones. They need to be clearly marked. However, the stroke on them does make them a little overpowering. I'll probably go back and pencil them in by hand.

Thanks for the catch.