Swim Wave Order

Yes, it does generally have to do with the assumed speeds of different groups, but races seem to vary in how they set this up. At some races you will see the younger (presumably faster) groups going off first, with novices/older groups/athenas and clydes going later. The rationale for that kind of set up is to keep the faster racers from running over the slower ones, or having to deal with all these people "in their way." Other races will switch this around, with the rationale being to not make the slower folks be out there all by themselves after everyone else is done. Race directors struggle with how to please everyone and what is the best way to keep everyone safe.