Battle of San Nicolás
1811 CE.
Shown on the map at -33.360°, -60.138°.
The Battle of San Nicolás was a naval engagement on 2 March 1811 on the Paraná River between the Spanish royalists from Montevideo, and the first flotilla created by the revolutionary government of Buenos Aires. It was the first engagement between the two fleets in the Río de la Plata region since the revolution, and a royalist victory.
Text from the Wikipedia article Battle of San Nicolás, licensed CC BY-SA 4.0.