Is there a code that prohibits a gfi with in a certain distance from a lake? I'm asumming it's 10 feet like a pool.
Nope, you can have a receptacle on a pier over the lake. Same with salt water.
If the installation is near a body of water as stated check article 555 to determine elevations from the water datum plane if applicable 555.19 ect.
note 555.1 says "Private, noncommercial docking facilities constructed or occupied for the use of the owner or residents of the associated single-family dwelling are not covered by this article."
You should still be aware of the artice though so you can make good "design" decisions.
See 682.15 in the 2005 NEC