Most adults who "cannot swim more than a length" can swim perfectly well. What they cannot do is breathe, and three specific faults cause almost all of it.
Fault 1: holding your breath
This is the big one.
Above water most people breathe in and out. In freestyle, you should breathe out continuously underwater, through your nose and mouth, so that when you turn to breathe you only have to breathe in.
Holding your breath means that in the fraction of a second your mouth is clear, you must exhale and inhale. There is not time, so you take a shallow breath, and carbon dioxide builds up. That is the panic feeling at the end of a length — it is not lack of oxygen, it is unexhaled air.
Practise this standing in the shallow end: face in, hum out slowly through your nose, lift, breathe in. Two minutes a session for a fortnight fixes more than any drill.
Fault 2: lifting your head
Turning the head to breathe is correct. Lifting it is not.
Lift your head and your hips drop, your legs sink, and you are suddenly dragging your lower body through the water. The effort doubles and you conclude you are unfit.
Rotate your whole body instead — shoulder, hip and head as one unit — and keep one goggle in the water as you breathe. If both eyes clear the surface, you have lifted.
Fault 3: breathing too late
By the time you feel you need air, you are already behind. Breathe on a rhythm rather than on demand — every two strokes at first, every three later.
Every three is worth building towards because it forces you to breathe on both sides, which keeps your stroke even. A swimmer who only breathes to the right develops an asymmetric pull without noticing.
What to practise, in order
- Bubbles standing up. Face in, hum out, lift, in. Two minutes
- Kick on your side, one arm extended, face in the water, turning to breathe. This teaches rotation without the complication of the arms
- Six-kick switch. Six kicks on one side, one stroke, six on the other. The drill that builds the whole rhythm
- Full stroke, breathing every three
The thing that takes longest
Relaxing. Tense muscles use far more oxygen than relaxed ones, and a nervous swimmer works twice as hard at the same speed. That improves with familiarity rather than with training, which is why swimming twice a week for a month beats once a week for two.
Coached swimming at KGB runs for all levels, including adults who are starting from the shallow end.