Swim course measurement

How are swim courses typically measured? GPS? SWAG?

It is obviously complicated as longer routes have multiple turns etc, but one would think point to point swims like Racine and Steelhead should be relatively simple to measure…no? Shorter sprints, like pigman, are simple - just a rope from the beach to the turn around with buuys tied a long it. That at least makes for a repeatable swim distance year over year. It seems this would make comparing PR’s on just about any two (or more) courses is not really all that reliable

when i was RD for the West Point (US Military Academy) triathlon back in 93 and 94 we used a laser range finder.

/r