It is worth noting that in bad weather conditions, such as rough seas, the underwater observatory closes due to poor visibility. This makes perfect sense of course, but was not something I had considered when planning our trip! We went into Busselton specifically to visit the underwater observatory and famous jetty. It was a very cold and windy day in June, and the sea was rough. So windy in fact, that they were considering stopping the little train too!
We had a nice fish and chips lunch and enjoyed a bit of a walk, but I did feel a bit silly for not even thinking about what the visibility would be like, given the winter weather. The pictures of the beach and jetty on the Internet are all taken on calm blue sky days, and I had foolishly imagined that it would be just like that. Especially after seeing how clear and blue the water at Rottnest island was, even on an equally cold and windy day!
Worth being aware of the changeable sea conditions, if you are planning your itinerary around visiting the observatory.