@Borkchop I'm sorry, I have looked on this, tested this map up to a 18k city, expanded tiles, laid some bridges down and I couldn't replicate any flooding. Actually land in this map is on averange +10-15 metres above water level. I'm aware of river months floods and I always try to 'break' the water stream with a small hill or an extra elevation on my maps, but in this case I can't find the problem. I really sorry if it messed your save in any way.

Great in overall look and organic flow of natural features but flooding, flooding, flooding! :( The river near in the starting location floods the opposite bank and the "point" on the highway side if you build bridges across it.