You have to make it fun. You might need to go in too. Or do you know someone with an older lab that loves the water?
When I tried to teach the pups to swim, they loved the water but wouldn't swim. Then when I took one of them out with their mom and they watched HER do it, Jed followed right in without a thought. I took him a few weeks later with our other female, and he swam right along with her too.
Your Lab is old enough. Some Labs jump in and swim immediately. Some never do without training.
Below is a copy of a post I've often made:
My Bess took to water immediately when she was about 5-6 months old and swam like a fish. It was sometimes a problem with her because she was magnetically attracted to swim in any water she saw, safe for her or not.
My Puff, on the other hand, likes to splash in water, wade in it, but was extremely reluctant to go any farther than have it just touching her belly. We first tried her at a lake with other Labs that swim. No luck. Next, I tried getting in the water and calling her to come to me. Ditto. (Not swimming wasn't an option since my sailboat is a great pleasure to me and Puff goes along.)
We use 2" x 12" vinyl "Lucky Dog" training dummies* which she retrieves. When she was about 8 months old we'd go for walks by ponds. I tied a 30 foot kite string to the TD so I could pull it back in case she didn't get it. (Wise decision; saved me from getting wet.)
I tossed it near the water's edge and then progressively farther out.
Puff took some extended effort to learn to swim properly. For one thing, she's a slightly small field line Lab and lacks much of the buoyancy many other Labs have.
Her first attempts at swimming were to furiously flail the water with her front paws but not use her rear legs. That put her in an upright position in the water. Putting a canine lifevest** on her solved that problem and with that she quickly learned to use her rear legs.
But Puff still lacks a lot of the buoyancy most other Labs have. Without her lifevest, when swimming only Puff's head and some of her neck is above water. With most swimming Labs, all of the top of their back and tail is slightly above the water's surface.
So swimming is not on Puff's list of "Top 10 Favorite Things To Do". Running and splashing at the edge would probably make it but not swimming.
* Lucky Dog retrieving dummies -- available at www.gundogsupply.com and many other online stores.
** canine lifevest -- cheaper ones (say $20-25 for growing dogs) are available at WalMart and PetsMart, and other places. Better quality, higher priced jackets (say for adult dogs that do boating) are available from RuffWear & Outward Hound for more $$$.
Puff [YF, AKC field line (from competing HT/FT breeder) 62 lbs, dob: 8-'01]