We have lakes, lots and lots of lakes of all different sizes. The reason (at leas according to what they told me in school) is the ice age.
The ice ran through the mountains of the nothern hemisphere and gouged out valleys and hollows, You can see them everywhere here, and left huge freshwater seas and lakes. These lakes drained at the end of the ice age but left millions of of smaller lakes scattered about. Since there is a lot of water coming in through rain and snow and less draining due to the shape of the ice age terrain and the colder climate, they're still around.
I grew up on a the bottom of a lake. A 5000 year old lake perhaps, but you can still take a shovel out into the area and find the old sediment layers and see where the shoreline were, it's alot dryer and less fertile soil. The big lake left a string of dozens of smaller lakes, from Hornborgarsjön to Lången.

A side note about the lake, a local amateur archeologist and historian called McKeys wrote a book where he fits the Beowulf saga in around this lake. if you belive his research (it's a bit sketchy but may be plausible) it would have taken place right in my back yard, he even points out a possible burial mound where he could have been buried.
Beowulf would have been called Björn thou, Beowulf=Bee Wolf (Biulv)=Bear=Björn
Now i'm rambling again.

There are lakes, lots of them everywhere. I think we underestimate how many bodies of water there is actually. If you have a nice depression with a trickle of water coming in, there will be a lake, or a pond, or a pool, or a swamp or a puddle.