Tomb Raider I - Unfinished Business (Lucky Diver Trophy)

Level 2: The Hive (Unfinished Business DLC) - Collect 11 items underwater without resurfacing.
This can only be done in the area just after you fight the 2 centaurs in the arena for the Ben-Hur trophy. After hitting the switches, you'll be in an area with a pool and 3 eggs. After defeating the enemies, it's suggested that you save so you can reload later and get your health items back (since you'll need to heal once you run out of air) while collecting everything at your own pace.
Dive in the pool and use the switches in front of you to open up the tunnels on either side. In the LEFT tunnel are 5 items (4x Uzi Clips and a Large Medi Pack), in the RIGHT tunnel are 6 items (3x Shotgun Shells, a Large Medi Pack, and 2x Uzi Clips).