Can not climb 1 block height if player is in water 5 or more blocks from water source

Can not climb out of a 1 block deep trench if water is level that is 5-8 blocks away from the source block.

Build a trench 1 block wide, 1 block deep and 6 block long.  Place a water source at one end, enter the water, can not exit at other end (with water level at 5 blocks away from the water source).  Same for 6, 7, and 8 blocks away