In a recent game I placed a city between rivers and now am unable to build anything. When I delete the forest NW of the city, I can build there; apparently my docks allow me to "cross" that particular river, but there is no way to cross the others. Now, that may make perfect sense in terms of gameplay (though I don't happen to like it), but what troubles me is that I could find no reference to this effect of rivers in the gameplay concepts section of the Hiergamenon (or anywhere else, for that matter).
Is this documented somewhere that I missed? Is it reasonable to ask that it be changed in the future?
A picture. Note empty list of what can be built.