The water has been filled into the lock on the right, making it level with the lake. Now the gates are opening to allow the approaching ship (from the left) to move towards the Atlantic.

An interesting note on the drive over to visit these Gatun Locks: On the road, as you approach Colon where Panama has created the 'Duty Free Zone' which is basically a tax-free exchange zone at the wholesale level, you see billboard after billboard advertising all of the shops and brands that are represented; and the billboards might be too racy even by American standards...quite the show.