The outpost (fortín) of Boquerón, among others, had been occupied by Bolivian troops since late July 1932 following instructions of president Daniel Salamanca, which led to the escalation of what began as a border conflict into a full-scale war.

The use of mortars, an unknown weapon for the Bolivian troops until then, would give the Paraguayans a decisive advantage during the siege.

Both sides suffered from the lack of potable water – the Paraguayans had to get it from a small lake at Isla Poí (50 km or 30 mi to the east), and although the Bolivians had wells inside their compound, they were under heavy Paraguayan fire and were eventually contaminated by the bodies of fallen soldiers.

On September 12 a 3,500-man Bolivian relief column coming from the southwest was driven back near the outpost of Yucra.

As the siege progressed the Paraguayans began to suffer from a shortage of water from Isla Poí due to over-extraction from the wells.