It originates in the Chilean Altiplano of the Arica and Parinacota Region, crosses the Andes and empties into Coipasa Lake in Bolivia.

The upper reach of the river lies within the boundaries of Lauca National Park in the Parinacota Province.

In this area, there is a type of marsh known as Parinacota wetlands, in which converge several streams, being the more important the river just mentioned, which has a variable flow rate ranging from 100 to 560 L/s, and an average of 260 L/s.

The spurs of the Cordillera Central (also known as Chapiquiña) form an obstacle impossible to pass through, forcing the river's course southward.

In the vicinity of Wallatiri volcano, the Lauca turns again, now eastward crossing from Chile into Bolivia at the latitude of Macaya, at an elevation of 3,892 m asl and with a flow rate about 2,6 m³/s.