Part of the challenge here is that this is a snippet of a larger map, making it tough to see where the rivers go and the lakes versus the seas... The rivers all follow the correct logic, and the lakes are mostly made obvious by the fact they are completely surrounded by land and of course, are named lakes. I wish that they effects were better show here, but the relatively low grade JPEG does not capture the subtleties of the effects very well. It is really a nice look.
Oh, and yes, that body of water to the top center left is a lake, with water flowing OUT of it to the main river flowing through this region (from the western mountains to the eastern ocean). It is a broad gently sloping central grassland with broad flood plains. Again, the larger map would have made that obvious.