Hi Sue,
I am not sure if anyone here has done Blue Lagoon w/o a excusion, because the only two ways I know of to get to that private island is by the Dolphin Encounter boat or a private boat that is used for their excusions. I did the swim with the dolphins a few years ago and at that time Disney didn't offer the excursion, so I had to figure out how to get their by myself (and I do mean just me...no hubby or anyone.) I learned from the taxi driver that over on Paradise Island is where you get the dolphin encounter boat (which is what I got on after checking in at their excursion desk). While on the island I didn't see any other boats except theirs and I was able to take a encounter boat back to the Carnival Ship (as they did offer the excursion at the time and they were docked next to Disney...saved me a few bucks on that return trip and some time too.) So, unless someone else knows differently, I would say the only way to get to Blue Lagoon Island is by an excursion of some type.
PS
I highly reccomend the swim with the dolphins encounter there!
Mmketeer Next cruise in Dec.2002