Lakes without rivers

[davidf]

I was reading the tutorial on How to get your rivers in the right place , and it made me want to learn more about lakes.

Up until now, I was happy with the idea of adding random lakes to a map (in reasonable locations), without rivers flowing into or out of them. But according to wikipedia, a "closed lake" will always be salty, which makes it sound like you wouldn't find them just anywhere -- for example, not in the middle of a forest (I assume).

An exception might be if there is an underground river flowing out of the lake. Not sure how common that would be, though.

I'm also wondering if a lake can remain fresh if there is a very intermittent outflow (e.g. only after heavy rain).

My main question is: in what situations would a lake that has no river flowing out of it look wrong to you on a map? Or a lake that has no rivers into or out of it?

[Charerg]

Well, technically almost all lakes have rivers flowing into them (the water needs to come from somewhere). I guess the notable exception would be crater lakes. So, if you want a lake without any rivers, the usual circumstances where one might exist would be a caldera or a crater (either from a volcano or a meteor impact).

Other than that, it all depends on elevation. Water always flows downhill, so if you have some kind of basin surrounded by mountains, then a closed lake would appear. As to the salinity level, that can vary, and I don't believe surrounding biome makes any difference. I'm fairly sure there are some closed lakes in Canada, for example, in the middle of the taiga. So, basically it all comes down to the elevation. One thing worth noting is that usually basins tend to fill over time due to erosion, and once it does fill, erosion will eventually carve a way out of it (which is why closed lakes are relatively rare).

Edit: One thing I might add is that closed lakes (at least major ones) seem a bit more common in dry and hot climates (Caspian Sea and the Aral Sea, to give the most notable examples). I think this is because a closed lake needs to have a balance between water evaporation and water inflow. In a more wet climate, or far to the north where evaporation is fairly minimal, it's more likely that the inflow will be greater than the evaporation, and therefore the lake will eventually overflow its boudaries to the point that it's no longer a closed lake.