Tom's points are well made on the whole "waders pull you down when they fill up" issue. When I was "squeezing fish for a living", I dove routinely in wet and dry suits in Lake Michigan, Huron, and Superior. A dry suit is essentially a "Michelin Man" looking closed cell foam dive suit that seals at the wrists and neck and has an attachment on the chest for your secondary low pressure line that comes off behind the first stage regulator on the air tank instead of using an external bouyancy compensator. My wet suit is a 3/8" Posiedon Brute Suit for cold water diving. Both require a mountain of additional lead, twelve and eight pounds respectively, to keep me at neutral bouyancy when submerged, in comparison to using a standard 1/4" chemical blown neoprene wet suit. You have to get down about 50' feet before the neoprene in a wet suit's internal bubbles compresses significantly...
Neoprene waders are the same closed cell foam, which adds bouyancy to an individual on immersion. The only apect of stepping over the tops of your waders that impedes your ability to swim on full immersion is the "trolling bag effect" imparted by open topped waders. If you wear a wader belt (Simms makes a really nice one with lumbar support pads that keeps your kidney area a little warmer in a layout boat and provides good lumbar support) cinched tight, even standard or Gore-tex breathables will lend good bouyancy to keep you afloat with minimal water intrusion. Simply pull your knees into your chest if you are in a current and work your way to shore. I have the dubious distinction of falling off slimy logs three times while electrofishing streams with a pulsed DC shocker running-not a fun experience, but not lethal either.
Cold water immersion carries a much greater risk of mortality if you go overboard, since massive vasoconstriction immediately occurs, making your heart work significantly harder to maintain blood flow to your extremities against this higher head pressure (preload increase). If you have significant background CAD, you run a much higher risk of a MI or sudden cardiac death event, should you go swimming unintentionally. A pair of fleece under-wader pants, in combination with neoprene waders that are close fitting and cinched by a wader belt tightly at your torso level, are a pretty decent offset to help keep you afloat following accidental immersion, as well as minimizing water intrusion and aiding in minimizing conductive heat loss increase when you get back on board.
Most of you likely recall the old saying: "Layout hunting is a waterfowling technique best practiced by individuals with currently paid-up life insurance policies!" Modern layout boats and tender equipment, as well as adequate precaution(s) and safety practices lower that background calamity risk...a pee bottle on board is also a good idea, which enables you to roll over onto your knees facing the anchor line whle relieving yourself.
That was the issue of the old Bankes pumpkinseed layout: to keep it from being designated a sinkbox, as well as allow an adequate sight field from the cockpit, due to their high freeboard design, the boats had a slightly too-high center of gravity, making them capsize prone in a heavy chop.
