you have a stopped up defrost drain. pull out bottom basket, look at the rear of the freezer section just below the panel. you should see a drain hole. the area around it will be frozen. you must open the drain. use hot water to melt the ice at the drain tube. most likely you will have to go behind the ref. and take the back panel off and the obstruction will probably in one of the curves.

the reason for the water is that when the box goes into a defrost the frost is melted of the coils and should drain in a pan under ref. when it can't drain the water builds and freezes under your basket. when the ice get's thick enough the defrost water runs over the ice and out the door. probably happens about twice a day. icemaker o.k.