Question
my house has a wet area by the mailbox that i had the city test for a leak.  they said it wasnt a leak, possibly a high water table.  my problem is the back of the house.  two levels down is my back yard, goes into a lake.  the yard is level, but behind the "retaining wall" it stays soggy wet until the dry season, then it does dry out.  is this a spring? or is it drainage coming down from the house etc that is pooling and collecting here?

Answer
It could be any of the things that you mentioned, high water table, a natural spring, runoff from another area or the roof, gopher holes filling up with water, and number of other things.  Its best to have someone who is familiar with local conditions come and look at the problem to really get to the bottom of it.