Arethusa Pool: How Did Mou Waho Get a Lake on Top?

New Zealand's Strangest Lake Address

Arethusa Pool sits at the top of Mou Waho, roughly 150 metres above the surface of Lake Wānaka itself. That makes it a lake on an island in a lake — a genuine geographic oddity known as a recursive lake, and one of only a handful anywhere in the world. Māori originally knew it as Moutimu; early European visitors later called it Paradise Lake, before the name Arethusa Pool stuck.

Carved by Ice, Not Volcanoes

Unlike a lot of small alpine lakes, Arethusa Pool wasn't left behind by a river or dammed by a landslide. It's a glacially-scoured basin, gouged out of the rock by the same ice-age glaciers that carved out Lake Wānaka far below it. As the ice retreated at the end of the last glaciation, it left behind a depression at Mou Waho's summit that filled with water and simply stayed there.

A lake, on an island, on a lake, on an island — geology's version of a Russian doll.

Small Enough to Miss, Strange Enough to Remember

Arethusa Pool isn't large — you could walk around the whole thing in a few minutes — and there's an even smaller rocky islet sitting inside it, adding one more layer to the nesting-doll effect. What it lacks in size it makes up for in atmosphere: still, dark water ringed by native bush, with the wider lake and the Southern Alps visible through gaps in the trees on the walk up.

Cold Enough to Notice

Swimming is allowed and genuinely popular on a warm day, though the water sits at a very Southern Lakes temperature — cold enough to sharpen the senses fast. Most visitors do it once, take the photo, and are perfectly happy to towel off and start the walk back down.

See it for yourself on our full-day lake tour, which stops on Mou Waho.