My 1 year old dog is half German Shepherd, half lab. He loves swimming himself, but today was the first time we had him out in the backyard while we had people over to go swimming in our inground pool. He was freaking out and barking/trying to jump in the water with the people swimming. We think he is doing this because he believes that they are in trouble. We have a vinyl liner in the pool so just letting him swim is not an option we are thinking of for an answer. Today we put him inside in the crate because he did not stop barking. However, since the summer is just beginning, we would like to have him outside enjoying the weather with us, with people in the pool!! Any suggestions on how to fix this would be great! Thanks!!
Have you gone through any obedience training? Try going through 15 minutes of basic training with him while people are in the pool. Get him to focus on you and go through sit, down, stay, whatever else he knows. It will take lots of repetition, but it will help him learn to focus elsewhere.
Try not to give him a command that you don't follow through with - such as being in the pool and telling him "no bark!" but when he continues to bark you stay in the pool. He'll learn to ignore you.
Also, nothing wrong with crating while you work on this. You don't want him to practice behaviour you don't want.