In the pool I swim in, a four-lane 25m pool near Aberystwyth, Wales, when the pool is set up for lane swimming, the lanes are designated as fast, medium, medium, and slow, but all these seem rather nebulous concepts and open to interpretation.There is no lane police. By skilful timing of my departures, I can usually fit in with the 'fast' swimmers, most of whom are considerably faster than I am. Sometimes the first medium lane is also occupied by fastish swimmers.The lanes alternate between clockwise and anti-clockwise, so that swimmers are not coming in opposite directions on either side of a lane line, thus avoiding bow-wave problems. Collisions are rare but not unknown, more commonly knuckle contact as two swimmers pass in opposite directions. This can be painful but not life-threatening. Butterfly and backstroke are best practised at the end of the session, when traffic thins out considerably.At weekends there is often a lane at one side of the pool for swimmers who wish to swim continuously or swim intervals. Often there are huge discrepancies in pace between the various inhabitants of the lane, which makes for variety, and sometimes frustration, but usually works out quite well.