How do I get my lab to enjoy swimming?

My chocolate lab loves when I throw the ball around outside to her, but lately it has been unbearably hot outside and she just gets exhausted. I bought her a decently sized blow up pool for her to swim in but she doesn't seem to like it. Every time she gets in she just hops right back out, i tried to throw the ball into the pool also for her to chase after but the same thing happend. Any suggestions? Thanks.