I went for a swim at Heros Beach last Friday evening and spotted two stingrays, one about 20cm across and the other about 40cm. It was about an hour after high tide and the water was very shallow.
I snorkel backwards and forwards across the bay for a bit of exercise. I use a snorkel to allow me to swim without turning my head to breathe- protecting an old whiplash injury. Besides the two stingrays, I saw many sudden clouds of sand where I had disturbed stingrays. I estimate that there were at least a dozen in the shallows. There were also plenty of bream happily swimming around me. They were mostly about 10 to 20cm long. You could just stand in thigh deep water and watch them.
We also spotted a small stingray in the shallows off Cove Boulevard last week. We once saw a huge one more than a metre across swimming off Cove Boulevard. Winter is the best time to spot them swimming as the water is usually quite clear in winter.