In the attached screenshot, you can see that I should be able to place an aqueduct adjacent to my city center and the two tiles the game recognizes as valid, but I cannot. Am I missing something? I was able to place an aqueduct in a different city on flat land, and there is no mention in the civilopedia about flat land anyway, so it cannot be that. It is adjacent to my city center and a river, and has no irremovable features (like swamp before getting irrigation). I tried reloading, but that did not help. It seems so oddly specific, because I can place aqueducts on similar tiles in other cities, and I don't know what makes this one different.