Is that a Real Lake?

One thing that I've often wondered when I've seen a lake is: Is it a "real" lake or is it a human made reservoir?

From the ground unless you already know, it's kind of hard to tell sometimes.

From the air and especially from Google Maps it gets much more obvious.

Natural lakes have rounded edges and look like they belong there.   This is Consultation Lake in the Mt. Whitney area in the Sierra Nevada.  Rivers enter and leave much the same way they came.  This particular lake was covered in snow when its satellite photo was taken so this is the map view.

Lakes created by dams have that stopped up bathroom drain look about them

This is O.H. Ives Lake in East Texas that I have only seen from a plane.

The fastest way for me to tell from the air is to look for that tell-tale straight line which is the dam.

This are some local resevoirs near me.  Briones and San Pablo:

Looking closer you can see the flat lines where the dams are located:

 Another way to tell a fake lake is to look at where you see where a river should be.

 
In the O.H Ives Lake pictured above, you can see two rivers streaming in, but only a ghost of one on the other side and sure enough that is where the dam is,  Zooming in on ghost river you can see a discontinuity that is the dam.

Another example is Red Bluff Resevoir:

Big River going in an just a trickle at the bottom.  Zooming in you see:

Some are harder to spot but you can using the same technique.

This is Shasta Lake in California.  It definitely has that plugged drain look about it.

There are several rivers so it takes some looking around to spot the affected river.

Looking on the West side there is a candidate on the bottom left:

And zooming in your see the dam:

But sometimes even natural lakes have human intervention.

Lake Tahoe is a gorgeous natural lake (http://en.wikipedia.org/wiki/Lake_Tahoe) 

But even it has a dam where they can control the lake's level. I couldn't see it myself, but the Wiki page says it's in Tahoe City and on closer inspection in that area you can see it:

So now you have something to obsess over when you're looking out  a plane window.  Of course most people just enjoy the scenery or read a book.