"Marina approved" power cords?

[Idaho Mike 29]

I got a letter from the dockmaster at the marina where I keep my boat advising:

You currently are using an electrical cord that is not "marina approved".  There are very specific electrical cords to be use on docks.  The current cord must be replaced with a "marina approved" electrical cord.  IF the cord is not replaced within 10 days of this letter, the Board will instruct the Dock master to replace it and charge you for time and materials.  

My setup from the shore power station, near the bow of my boat on the slip, is to run a marine pigtail adapter (2' long) to a heavy duty extension cord, which then goes to my battery tender.  I'm not sure if they are worried about it not being beefy enough, or whether they want to see some sort of GFCI / fuse that is specific to marine extension cords.  Is there such thing as a standard wall-outlet style extension cord like you use for a standard 110 V. system?  It seems all the true "marine" grade extension cords have the circular 3-hole plugs on both ends.

[InfinitySurf 302]

Sounds like they are actually talking about the cord, tho I would think what matters is where you plug it in being a GFCI that will trip if it comes in contact with water.