Went to refill a bottle in a pond, got to that swimming depth, realised I didn't have the bottle on me, turned around and swam out. I wasn't in the water any more than 5 seconds but I lost all my gear except for a pistol and a few clips. Doesn't really make sense considering a pack is strapped to you in at least 1 place, sometimes 2. An alternative might be a fatigue system, where a swimmer becomes tired and prone to drowning the longer they're in the water. Maybe the rate this fatigue sets-in can be proportional to the weight the player is carrying. This way, players have to decide whether to continue swimming and risk drowning or sacrifice some gear to slow the fatigue rate down. Most other things in the game have the players striking balances with the gear they choose to have (ammo versus medical supplies and food, etc). I just thought this would gel nicely with that model.