Chile took its South American neighbor to the International Court of Justice (ICJ) in 2016, asking the court to declare the Silala an “international watercourse” and give it equal rights to its waters.
It is the latest in a series of disputes between parched Chile and landlocked Bolivia, which have been vying for access to the Pacific Ocean for nearly 150 years.
The Silala originates in the high altitude wetlands of Bolivia and crosses the border with Chile, flowing for about eight kilometers.
Bolivia considers that the Silala has been artificially diverted by Chile thanks to a system of canals built to collect water from springs and is demanding financial compensation from its neighbour.
The judges of the ICJ, which sits in The Hague, will deliver their verdict at 3 p.m. (1400 GMT).
Both countries have a long history of litigation before the ICJ, created in 1946 to settle disputes between states.
Former Bolivian President Evo Morales had sought to use the river controversy as a bargaining chip in a separate case before the ICJ, in which La Paz demanded to compel Santiago to negotiate sovereign access to the Pacific Ocean.
In 2018, the ICJ dashed La Paz’s hopes of regaining access to the sea, which it lost during the Pacific War of 1879-1884.
At the time, Mr Morales threatened to reduce the flow of the Silala in Chile’s arid Atacama Desert and impose fees for its use.
– Climate change –
Relations between the two countries have been suspended since 1978 due to the border dispute over access to the sea.
At the last Silala hearings in April, Chile’s representative Ximena Fuentes said La Paz’s demand for Santiago to pay for the use of the Silala River was “absurd”.
Faced with the consequences of global climate change and the scarcity of fresh water, “countries are called upon to cooperate in the effective management of shared water resources”, added Ms. Fuentes.
Bolivia retaliated, saying Santiago’s case was “hypothetical” and that it had “never” done anything to block the flow of the Silala into Chilean territory.
ICJ judgments are binding and cannot be appealed, although the court has no real means of enforcing them.
Water is a major issue at a time when climate change is having increasingly serious effects.
Chile is currently going through a 13-year “mega drought”, the longest in at least 1,000 years, which threatens the country’s freshwater resources.
In Bolivia, the Pantanal – the world’s largest wetland that also spans Brazil and Paraguay – is experiencing its worst drought in 47 years.