The Ralja originates in the northern part of the Kosmaj mountain, north of the village of Velika Ivanča, in the Sopot municipality of the City of Belgrade.

At the villages of Popović and Mali Požarevac, the Ralja turns straight to the east for the rest of its flow and also from this point, the Belgrade-Niš highway joins the railroad.

In July 2021, city announced that project for flash flood warning system is being applied on several rivers and streams on the territory of Belgrade, including the watershed of Ralja.

[2] By March 2023 three hydrologocal stations were placed along the river, at Dražanj, Umčari and Živkovac, while the fourth was placed at the confluence of the Kamendol creek.

Measurements from October 2021 and August 2022 showed high and prohibited levels of cadmium, lead, copper and zinc in river's mud.