I also thought it was coastal and it took me ages to identify the location on the map of Faerûn that I found; not really helped by previously having zero experience of the place; and that the map significantly pre-dated BG3. While I haven't personally seen sandy beaches along rivers (just swamps; in fact Jarrow, the town where I was born, is thought to be named as such) I'll defer to other people's experiences, and only after locating it on the map did I zoom in to see that it is indeed a river, and a remarkably impressive one at that. Then again I have seen some IRL that are similarly impressive even far inland, such as the Severn.

J'aime le fromage.