 Even with the city under siege from land, the royalist naval squadron maintained the naval supremacy over the waterways, the Río de la Plata and the Uruguay and Paraná rivers.The Montevidean squadron under Jacinto de Romarate destroyed the first flotilla from Buenos Aires, which went up the Paraná River carrying reinforcements to the Paraguay campaign, at the Battle of San Nicolás.After that victory, Montevideo's naval forces could then establish a blockade of the port of Buenos Aires, effect a bombardment and avoid the fall of Montevideo.