The governing body for world swimming requires that an Olympic-sized pool have eight lanes and be exactly 50 metres in length, but they also recognise pools that are only 25 metres long.

Records set in ‘short course’ pools are kept separate from those set in official 50-metre pools because it may be advantageous for swimmers to have more or fewer turns in a race. This differentiates a swimmer’s qualification time obtained in long and short course pools. So what’s all this got…