First Basin at the Cataract Gorge in Launceston has an open air pool on a grassy reserve beside the freshwater basin itself. There is a kiddie's pool and play equipment too, so the park is pretty perfect for families on a warm day during the summer school holidays. I had a dip in the swimming pool, but it was far too busy to swim a length or two.
View of First basin from the Zig Zag walking track
I'd really come here to swim in the basin itself though. There were a few people in already, including kids with inflatable rafts and teenagers jumping off the low cliffs into deep water. I swam along the southern shore and back in water that was just a little chilly.