The following reports admittedly stretch what can be considered cryptozoological. There is no doubt the animals in question are of a known species, but the identification is uncertain, the location in which they were observed was unusual, and no physical evidence was collected. I hope the authors don't take offence to my categorization, it is merely to demonstrate that investigating unusual reports is not some joke, and even without 'hard' evidence the investigation can be worthy of publication in a peer-reviewed journal.
My thanks to Markus Bühler for directing me to this story. All references from Alava and Carvajal (2005) until otherwise noted:
In December 1998, communities along the Babahoyo River, (Ecuador) were alarmed to see an unusual animal in the water, which a local television station managed to tape. The animal appeared to be a pinniped, and with a large head, large eyes, and absence of external pinnae, the authors and a marine mammal specialist identified it as an elephant seal (Mirounga), probably an immature male 4 years of age. A subsequent 8 hour survey of the river failed to locate the animal.
In February 2002, an elephant seal was observed in an estuarine area in Guayaquil city, first near a power plant and then in a shrimp farm. The individual was lying on the bottom of the shrimp pond (partially submerged), and was estimated to be 3 meters long by workers. The authors observed the animal while in a narrow creek near the farm and took photographs for future identification, where they once again reasoned that it was an elephant seal.
For those out there that didn't click on the maps, the first sighting occurred about 75 miles (120 km) upriver, while the second was about 50 miles (80 km) up but was over a mile (1.6 km) into a salt marsh.
How many animals were involved? The authors don't bring it up directly, but say "these two individuals" at one point. It would seem remarkable for two separate individuals to wind up in the same river system, although it is more parsimonious than assuming one individual survived the excursion and for some reason returned. As for the species...
Both events took place during the Southern Elephant Seal (Mirounga leonina) moulting season and La Niña events (Alava and Carvajal 2005), which was previously linked to the presence of Otaria flavescens in the region (Felix et al. 1994). Elephant seals are of course far from indolent beach blobs, and Alava and Carvajal (2005)'s review of the literature reveals both species can migrate thousands of kilometers, although the Southern species (M. leonina) appears to migrate more extensively and the Northern species (M. angustirostris) has not been observed to wander out of the North Pacific. Southern Elephant Seals have been observed off the coast of Sawqarah, Oman (Johnson 1990) and 46 (!) records are known from Brazilian coastal states, up to Pernambuco and the Fernando de Noronha archipelago (de Moura et al. 2010)), which demonstrates that the species can reach the equator. The authors cautiously suggest their records are the northernmost yet of juvenile southern elephant seals, but cannot reject the possibility of the southernmost record of the northern elephant seals (Alava and Carvajal 2005). It could be possible that both occurred, but in all likelihood the same species was drawn to the same region for some obscure reason.
As far as other instances of elephant seals in cryptozoology, Roy Mackal once hypothesized that the White River monster was a very wayward elephant seal - wayward in that the sightings were in Arkansas! One blogger hypothesized that a monster seen in the Solimões River was a wayward northern elephant seal (thanks to geographical confusion), but it could be possible for southern elephant seals to enter South American rivers - it still doesn't explain the reported small eyes, snake-like neck, and incorrectly reported country for the river.
Alava, J., and Carvajal, R. (2005). First records of elephant seals on the Guayaquil Gulf, Ecuador: On the occurrence of either a Mirounga leonina or M. angustirostris. The Latin American journal of aquatic mammals 4(2): 195-198. Available.
de Moura, J., di Dario, B. Lima, L., and Siciliano, S. (2010). Southern elephant seals (Mirounga leonina) along the Brazilian coast: review and additional records. Marine Biodiversity Records 3, doi: 10.1017/S1755267209991138
Secondary References (cited by Alava and Carvajal 2005):
Felix, F., Haase, B., Samaniego, J., and Oechsle, J. (1994). New evidence of the presence of the South American sea lion Otaria flavescens (Carnivora Pinnipedia) in Ecuadorian waters. Estudios Oceanológicos 13, 85-88.
Johnson, D. (1990) A southern elephant seal (Mirounga leonina) in the Northern Hemisphere (Sultanate of Oman). Marine Mammal Science 12: 242-243.