I think I have now completed this puzzle, but my solution throws up a few anomalies. In my solution I have coloured a total of 31 cells. I could reduce this to 30, or 29, by making the river move diagonally. It would have been helpful if the preamble had stated how many cells are to be coloured, but the fact that it doesn't leads me to assume that it is not critical and that any of the various options would be allowed by JEG. Also, in my solution the river takes a course in the north eastern corner that is not supported by the maps and I have a choice for the final cell. Again I assume that either would be acceptable to the checker. Do other solvers have the same anomalies, or have I got it all wrong (again)?