[dunkelgrun]

I used Gaussian blur 0.3 on a 1-pixel river and got the same as already said. I then merged another copy of my originial on top of the blurred layer and repeated the Gaussian blur.
It looked a whole lot better in places; narrow continuous rivers for the most part, but still dead staight N-S and showing pixellated edges elsewhere.

My original rivers had corner-to-corner pixels on the diagonals; I'm upgrading them to eliminate these and ensure that all pixels meet the next side-to-side. Then I'll try again :roll: .

:cheers: