I guess it could come down to how trained you are and how you would act...
“The next emergency landing I will cover is the WATER LANDING. If you are drifting towards a body of water, immediately look then slip away. If you cannot avoid the water, look below you to ensure there are no fellow jumpers and lower your equipment. Next, jettison your helmet, making a mental note of where it lands. Activate the quick release in the waistband. Disconnect the left connector snap and rotate the reserve parachute to the right. Seat yourself well into the saddle and activate the quick release in the chest strap completely removing the chest strap from the chest strap friction adapter. Regain canopy control. Prior to entering the water, assume a landing attitude by keeping your feet and knees together, knees slightly bent and place your hands on both leg strap ejector snaps. When the balls of your feet make contact with the water, activate both leg strap ejector snaps, arch your back, throw your arms above your head and slide out of the parachute harness. Be prepared to execute a proper PLF if the water is shallow.
Swim upwind, or upstream, away from the canopy. If the canopy comes down on top of you, locate a seam, and follow it to the skirt of the canopy.â€
So basically all your equipment is attached to you in such away you can lower and jettison it from the parachute harness in seconds. It's designed that way so you don't land on something harder and bulky during your Parachute Landing Fall (no skydiver style standing landings, you hit and let yourself roll onto your side and back to absorb the impact, you do NOT want to do that on top of your rucksack lol). So you lower your equipment and activate a couple quick releases (if you only have one in the harness and it fails….) and activate the last straps as you splash down so ideally you just slide on out of the harness and swim away.
Contrary to popular belief it's not really all that hard to swim or even float in uniform and boots. Heck we've trained swimming in pools with all that plus load bearing gear and rucksack. If you pack your ruck the right way it'll even float! Though thankfully after 9 years in the Army, including 3 deployments and 26 jumps the only time I've ever had to do that was at a pool specifically training for that.