The Río Sis is a river in Southwest Guatemala. Its sources are located in the Sierra Madre

Sierra Madre de Chiapas

Sierra Madre is a mountain range which runs northwest-southeast from the state of Chiapas in Mexico across Guatemala and into El Salvador and Honduras. Most of the volcanoes of Guatemala are a part of this range.A narrow coastal plain lies south the range, between the Sierra Madre and the Pacific...

 range, on the slopes of the Santo Tomás and Zunil volcanoes in the department of Suchitepéquez

Suchitepéquez (department)

Suchitepéquez is one of the 22 departments of Guatemala. Its capital is Mazatenango.It is situated in the southwestern region of Guatemala, limiting to the north with Quetzaltenango, Sololá and Chimaltenango, to the south with the Pacific Ocean, to the east with Escuintla, and to the west with...

. It flows southwards through the municipalities of San Francisco Zapotitlán

San Francisco Zapotitlán

San Francisco Zapotitlán is a municipality in the Suchitepéquez department of Guatemala....

, Cuyotenango

Cuyotenango

Cuyotenango is a municipality in the Suchitepéquez department of Guatemala.Cuyotenango was founded around the 16th century, and it's name in Nahuatl literally means "Fortification of the Coyote", name given by the Mexican soldiers accompanying Pedro de Alvarado, the Spanish conquistador of...

, San Lorenzo

San Lorenzo, Suchitepéquez

San Lorenzo is a municipality in the Suchitepéquez department of Guatemala. It is situated at 220 m above sea level. It contains 7,753 people. It covers a terrain of 60 km². The annual festival is on February 2.-External links:*...

 and Mazatenango and joins the Icán River

Icán River

The Río ícán is a river in Southwest Guatemala. Its sources are located in the Sierra Madre range, on the slopes of the Santo Tomás volcano in the department of Suchitepéquez. It flows southwards through the coastal lowlands of Suchitepequez to the Pacific Ocean.The river runs more or less parallel...

 which flows into the Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

.

The Sís - Icán river basin covers a territory of 919 km².