@Jshoer:
I was thinking that the lake I could leave that lake as it is, (or maybe could have several underwater caverns), I have to be honest: I´m still not 100% sure what I want about this map, so I´m just working on it as I go. But tonight I´m gonna work on some outflows to see if I get convinced about having one there, perhaps one that goes directly to the mountains would be a best option.

@Waldronate:
I have no idea about the scale of this map, perhaps it could be in between 115 Kms and 125 kms (71.4 miles to 77.6 miles). For the map that you mentioned I was thinkign in making some sort of a swamp and I wanted a decent area for it, of course, its not carved in stone yet so it may change at the end. I´m gonna work on the shading today for sure, I usually leave the rivers and lakes after I get at least mountains and terrain done, just in case that want to change something that could affect the flow of the river or maybe the shape of the lake. I´m totally open to any ideas about this!