It may be a blocked drain hole...
Modern fridges have an auto defrost feature to periodically get rid of any ice that may have formed - not the freezer but the fridge. Usually the water drains out through a hole at the back and runs through a small tube to evaporate on top of the motor/compressor unit unless... unless the drain hole is blocked - in which case it will gather in a puddle at the bottom of the fridge.
Empty the fridge, give it a good clean and gently poke something flexible down the drain hole.
Peccavi, October 2009
