Two North American Protestant ministers were sent by the ABCFM (American Board of Commissioners for Foreign Missions) in 1833 to Patagonia.
They were to stay among the native Patagonians and study the feasibility of setting up a mission there.
Their original plan was to land on the Chilean coast south of Chiloé, but lack of transportation made them change their plans and land at the Strait of Magellan, at Gregory Bay. There they stayed with a group of Southern Tehuelche natives.
These two brave (and I would add, reckless) men were William Arms and Titus Coan.
Both managed to survive where others had been taken captive and after three very difficult months, they reembarked back to the U.S.
The ABCFM after receiving their report decided not to establish any missions in Patagonia.
Neither of them reported any strange beings or cryptids during their stay in Patagonia, however, Arms' diary has a strange remark which I quote below.
It happened in the Atlantic Ocean, close to the coast of Buenos Aires, north of Patagonia, some parts of the text are, regrettably illegible but they seem to indicate some kind of "sea monster".
I have translated it from Spanish into English:
That afternoon [Captain Benjamin Pendleton of the "Hamilton"] described an [illegible] that he saw in the waters off the River Plate, saying that in total it was ten meters [33 ft.] above the water, nearly round and some twenty meters [66 ft.] from its tail to its head; it had long arms like fins with spines 50 cm [20 in.] all above its back. Algae had grown on it up to a great height.
Could it have been an Oarfish a "sea serpent" (actually a fish that looks like one)?
 Titus Coan (2006). Aventuras en Patagonia. Un viaje de exploración de dos misioneros norteamericanos. Noviembre 1833 - Marzo 1834. B. Aires: Zagier & Urruty Publ. pp. 242
Copyright 2009 by Austin Whittall ©