Flowing through the countries that once made up the republic of Yugoslavia, the majestic Sava river inspires a kind of serene continuity in a region marred by geographical and political division. Whether taking in the lush vegetation from above or plunging into the cerulean water, the camera in Matthew Somerville’s loving ode is in awe of Sava’s beauty. Here is a river goddess – and a historical witness.

Starting in Zelenci in Slovenia, Somerville’s cinematic odyssey drifts downstream along the entire length of the river, finally alighting at Belgrade, Serbia. Stopping along the way to interview the locals, the film brings up complicated ideas about nationhood, especially in countries where more and more people are leaving for a better future. Filled with troubling disdain towards refugees, a conversation between two Slovenian boat operators seamlessly transitions into a dressing room in Zagreb, Croatia, where a group of drag performers are preparing for their next show. Placing conservative nationalism and queer solidarity side by side, it is a startling juxtaposition that shows how loss and nostalgia can easily morph into bigotry.

Hanging over these intimate conversations, which bring together people of very different age groups, is an overwhelming sense of disconnect, either from an uncertain future or a past national identity that no longer exists. Commandingly narrated by the late Mira Furlan, Sava’s supposed inner monologue steadily reiterates a mantra of self-affirmation. “I am Sava,” she says repeatedly, with the assured timbre of a protective guardian. By lending the river a voice, Somerville’s film heightens its mythological presence, something that provides a feeling of unity to a fractured landscape.

• Sava is released on 21 September on digital platforms.