When Summer gets up to get her camera, she only appears to put her left shoe on. As she walks to her room, she is wearing both of them.
After the ship leaves the dock, it goes down a very wide canal, but one shot shows it still close to the dock on the starboard side.
When C.J. first responds to the water rescue, there is a male lifeguard on her boat. Once she gets to the scene, there is only her and Stephanie on the boat. Given the circumstances, t's unlikely they would have taken the time to change personnel.
When Matt and Summer get out of the lifeguard truck to go rescue the skydiver, Summer is obviously played by a stand-in. She has longer hair and is taller than Nicole Eggert.
Mitch says "Captain" Thorpe gave permission for the lifeguards to go on the cruise but by this point in the series Don Thorpe had already been promoted to "Chief".