Do you want the reason or the rationale? The reason is bottom-up design. The rationale is that there is an ancient, mostly eroded mountain range that runs N-S through the northern Almalen Forest. The lake and river that merges with the River Almalen just before it enters the sea are in what used to be an old subduction zone--the medium-sized central peninsula east of that lake will one day break off into its own island, having changed direction millenia ago.

Or something like that, anyway. I imagine if I'd started the map with the geology things might be different. But I didn't. So they aren't.