It seems unusual for a dog to seem to love swimming when he’s in the water but to not actively go in the water himself. There are just a few reasons why I can think this is the case. The first being that maybe he does not actually like swimming, and simply swims when you put him in the water because what other choice does he have? But from what you say this seems unlikely. You did not mention how you put your dog in the water. Do you just "drop" him in? Do you carry him in? Or is there a set of steps?

This might be important if the reason he is not keen on entering the pool is because he doesn’t like getting his ears wet, or at least water in his ears. It might be that the only time this happens is when he gets into the water. In this case, I’d suggest gently lowering him in or providing some kind of ramp that he can launch himself into the water from.

My last suggestion is simply that there is something daunting about coming off the side of the swimming pool into deep water. Most dogs’ experience of swimming is walking into a river or lake and gradually building up depth. Your dog’s experience might give him a feeling of loss of control. In this sense, it would also be great if you have a set of steps leading into the pool. If you do, then teach him how to use them. If not, I think the only solution is to gently lower him into the pool yourself.