Originally Posted by
audiojan
It depends... if you're comparing pool swim in jammers and lake swim in a wet suit, you might be just as fast. But, only if you are an experienced open water swimmer. Sighting (navigation) is a skill that takes time to learn and without it, you will very likely not swim perfectly straight in OW and thereby loose significant time. Also, if you're not used to OW, you might tighten up and loose time that way (very common for the first few times in OW).
The swimming technique translates from pool to OW, but that's about it...
I tend to agree. I prefer open water and only pool swim in the winter. Every year I see pool swimmers entering the ocean for apparently the first time. They have the strength and stamina, but are often confused by the moving waves (which you don't have in the lake) and swirling currents.
The bigger confusion factor is navigation; finding your mark and swimming a straight line to it. There are no lines on the bottom of a lake or ocean, and often the visibility is such that you cannot sight on anything underwater anyway. You have to learn to find objects on shore and line them up in a glance to hold a course. I think also the limited visibility underwater might freak out some swimmers not expecting that. (the black water thing someone mentioned)
The big key to OW navigation is finding something you can see every couple of breaths and sighting that reliably. I turn my head both ways when I swim, so I have learned to sight objects to either side to keep me lined up, and to have a set of objects in the direction of my goal that I can sight and line up to verify my track every now and then. Learn to do that and you should be well prepared.