I think that also the AI use of the river should be checked, I don't know if it works in another islands rivers but there AI does'nt move in with crcc or rhib in the river so I don't know how to fix, increasing river deep or making another thing to fix.
I will try Island pantera for check if the river can be used by AI ships
fixing swamp holes is a nice new I've based a mission starting there ...
thank you for your effort this is a really nice island!!!!