For a sand island Fraser has a quite astounding number of lakes, of three different sorts. The collection is unique in the world. There are ‘perched lakes’ high in the dunes, formed when an impermeable hardpan of organic debris develops in a dune hollow, fed entirely by rain. There are ‘window lakes’, forming where the land surface dips below the water table, and there are ‘barrage lakes’ formed when a mobile sand dune blocks a watercourse.

Here is Lake Wabby, both a barrage lake and a window lake:

 

 

This is about 8m deep and full of fish. You can get some idea of scale by the two people (dots) just visible on the lakeshore behind me. This lake will have vanished in 20 years, buried by this sandblow:

 

 

And here is a perched lake, Birrabeen:

 

 

It really is exactly this colour, but is only about 3m deep. And lovely and warm, absolutely requiring a swim. Here is Ali in it, demonstrating her latest bathing costume: