I think the problems with lakes is that people sometimes think of ponds as lakes and then what is the scale of the map. On continental style maps, most lakes would not be seen at that scale. On a regional scale, then, lots of lakes would be seen. On a city scale you could put in as many ponds as you like. Now this is all for a certain amount of realism. If some lake or pond happens to be quite important and you want to put it in, then you're getting into the representational realm and away from the realism. It's the balance that's hard and sometimes we have to compromise one way or the other for the sake of the story.

My 2 bits