I cycle a lot, I run a bit, and I swim once per week. I have been training once per week for 5 months now. When I started, I could barely swim a length of freestyle. Now I can swim a lap with ease.
However, I am struggling to swim more than a single lap without stopping at one end. Now I know what you're all thinking: form and efficiency. I don't think this is the primary reason for my poor swimming performance, as I have focused on efficient form from day 1, and have had others verify that my freestyle technique is smooth.
My question is, is swimming fitness that much different to cycling and running fitness? Is this normal, and why is this the case?