Continuity mistake: As the raft starts to sink, Lovey goes into the water on the back side of the raft. When the camera is in a close up of Mr. Howell, she's sitting beside him again. Then she's neck-deep in the water in the next wide shot.
Other mistake: As the girls are trying to land their catch, the Skipper comes by and starts to help. Although he was walking by, when he starts to help, his pants legs are already wet from previous takes.
Answer: Bob Denver answered this when he was on a talk show hosted by Pat Sajak. He said they were going to write into an episode where the castaways found all these clothes, but it got too complicated, so he said, they decided, "who cares, it's only a TV show," and forgot about it. So the writers and actors even asked this, they just never bothered to address it.