Excess water in botom of fridge?

Hi, I have a built in diplomat APM 6528 fridge with ice box.
Excess water keeps accumulating at the botom of the fridge by the two salad draws (about 20mm deep).
I have tried to cleer a drain hole at the back but this doesn't achive anything. I cannot understand how the water is being generated.
Can tou please give any advice.

Many thanks.