Near the big generator
In the small room, locked with a door code
In the female toilet
In the area with two splicers in water - on a bench to the right
Just after you pick up the rivet gun - take a right
On the bar, behind the stairs in the large area
When you start walking under water for the first time, there will be a damaged bathysphere to your left with two corpses - the diary is on one of the corpses