I can really recommend Glemaray at Woodford, it is definitely worth the time to get there.
My boy wasn't fussed with swimming at the start - he liked having his feet touching the bottom - now he eagerly dives in safely from the ramp to chase his "wubba" and get his exercise. I think my girl was a beaver or a seal in another life - she took to the water straight away and keeps swimming for the entire session. I also get my exercise trying to keep ahead of her.
You also have the option of increasing their workload with the spa bubbles and/or swim jets if required - BTW the spa is good for human legs after the work. There is also the facility to rinse them off afterwards or there is the option of having a hydrobath as well.
Needless to say, both my dogs now love swimming in any location - pool, river, surf. We just have to watch out when we visit grandma's pool - they think it's an open invitation to jump right on in.
Enjoy your swimming wherever you may go - it's great fun and takes a bit of pressure off joints - both dog and human.
Intruders & the BSDs