A very good travel tip is to snorkel at the bays of Exmouth. In Exmouth you'll find all you need from hotels, hostels, backpackers & camping grounds. Then you just need a car to get to the spots. Snorkels and fins are easy to buy/hire at your accommodation or at sport shops in town. 

I would recommend you to drive to the lighthouse and to keep on that road until you reach the Turquoise Bay, around 60km from Exmouth. That spot could be a bit touristy, but I would recommend you to check it out first. The reef is about 5 meters from the beach and you will flow with the current around 30 - 60cm above the corals. Awesome! After 200 - 300 meters you just get out, stroll back along the beach and start from the beginning again!

You'll see so many fish, corals and if you're lucky even a friendly reef shark. But these actually are quite shy and are getting out of your way as they are frightened of you. We've seen one, but that was just for a second, which was just enough time for a picture. 

There is also a small bay where you can snorkel without any current. I've seen a turtle here, a sea snake and many fish. 

If the Turquoise Bay is crowded just drive another 10km to the Sandy Bay, which I've heard is also very nice and not so crowded.