Before we went off to Sprengisandur we passed Þórisvatn the largest lake of Iceland, situated at the south end of Sprengisandur highland road within the highlands of Iceland.

Þjórsá is Iceland's longest river at 230 kilometers. It is in the southern region of the island. Þjórsá is a glacier river has its source on the glacier Hofsjökull. It flows out through narrow gorges in the highlands of Iceland. Further downstream, another river, the Tungnaá, flows into it (see also Háifoss), before it enters the lowlands. There it passes the valley of Þjórsárdalur (Thjorsardalur) where the historical farm of Stöng is located. In the lowlands it flows along the eastern border of the Great Þjórsá lava.

On our way to Sprengisandur its origin Hofsjökull was permantly the left.

It is a reservoir of a surface about 88 km² and uses the energy of the river Þjórsá, which comes down from the glacier Hofsjökull. Here in the south, it is exploited in a power station. Like a lot of other Icelandic lakes, which are mostly glacial lakes or volcanic lakes, it normally has a stark green color.