This is Buffelspoort dam. My parents-in-law are the managers there. It's a popular dam for skiing and fishing. Whenever we go there, my children always ends up in the mud, so I always take along their oldest clothes!
The poem is by Zilpha Keatley Snyder and goes like this:
Wherever, when'ver, whyever it goes,
Stirred by your finger or strained by your toes,
There's nothing sloppier, slipperier, floppier,
There's nothing slickier, stickier, thickier,
There's nothing quickier to make grown-ups sickier,
Trulier coolier,
Than wonderful mud!