It flows about 20 kilometres (12 mi) from the Stíflisdalsvatn [is] [ˈstiplɪsˌtalsˌvahtn̥], a small lake northwest of the Þingvallavatn, into the Laxárvogur [is] [ˈlaksˌaurˌvɔːɣʏr̥], a cove on the Hvalfjörður fjord.

[3] Other tributaries include the smaller Svínadalsá [ˈsviːnaˌtalsˌauː], Hálsá [ˈhaulsˌauː], and Þverá [ˈθvɛːrˌauː], all of which flow into the upper section of the river below the Þórufoss.

[1] The Þórufoss [ˈθouːrʏˌfɔsː] is an 18 metres (59 ft) high waterfall, located about 1.5 kilometres (0.93 mi) downstream from where Laxá í Kjós flows out of the Stíflisdalsvatn.

A further 6.5 kilometres (4.0 mi) downstream from the Þórufoss is the Pokafoss [ˈpʰɔːkaˌfɔsː] a rapids-like small waterfall with a 2 metres (6 ft 7 in) cascade.

The Þórufoss was the filming location for a scene in Game of Thrones ("The Laws of Gods and Men:" Season 4, Episode 6) where a dragon attacks a herd of Meereen goats.