linguistic:paraphrasing
Río de la Plata

The fleet sailed south along the South American coast, hoping to reach el paso, the fabled strait that would allow them passage past South America to the Spice Islands. On 11 January, a headland marked by three hills was sighted, which the crew believed to be "Cape Santa Maria". Around the headland, they found a wide body of water that extended as far as the eye could see in a west-by-southwest direction. Magellan believed he had found el paso, though in fact he had reached the Río de la Plata. Magellan directed the Santiago, commanded by Juan Serrano, to probe the 'strait', and led the other ships south hoping to find Terra Australis, the southern continent which was then widely supposed to exist south of South America. They failed to find the southern continent, and when they regrouped with the Santiago a few days later, Serrano reported that the hoped-for strait was in fact the mouth of a river. Incredulous, Magellan led the fleet through the western waters again, taking frequent soundings. Serrano's claim was confirmed when the men eventually found themselves in fresh water.