User blog comment:AgentG231/What specifically is the bug in the Animus 1.28 that made Altair can't swim?/@comment-4699238-20130425063554

it wasn't a bug, he lived in an area where it's hot, dry, and not much water, the only water where he lived was waaaaaay down in a valley from masyaf, so obviously they wouldn't have taught them to swim.