Þjófafoss is in the river Þjórsá, to the east of Merkurhraun lava field. The name of the waterfall translates as “thieves’ waterfall”, as thieves used to be executed by drowning in its pool. The waterfall is one of the three main waterfalls in Þjórsá. The Þjórsá river forms the boundary between Rangárvallasýsla and Árnessýsla and is the longest river in Iceland.
Þjófafoss is to the south of Búrfell mountain, not far from the Búrfell Power Plant and somewhat lower down from Tröllkonuhlaup in Þjórsá. The flowrate in Þjófafoss is rather low during winter but greater during the summer. This is due to the power plants on the river, as a large proportion of the water is diverted past the falls. The river is dammed at Sultartangi, forming the Sultartangalón reservoir. The water is first channelled through Sultartangi Power Plant and then into the Bjarnarlón reservoir and through the Búrfell Power Plant. As a result, it is first and foremost when the Sultartangalón reservoir is full in late summer that the excess water can flow over Þjófafoss.
With the construction of the Búrfell Power Plant 2, water flow over Þjófafoss will decrease even more, both during summer and winter.