Nahuel Huapi: the movie "Bajo Superficie" and the Aquatic tortoise or turtle theory

An Argentine documentary titled "Bajo Superficie" (Under the Surface) shot during the COVID-19 pandemic and released in 2022, explores the mystery of El Nahuelito, the mythical lake creature of Lake Nahuel Huapi.

You can see the full movie online (in Spanish). It is a 2 hour 20 minute-long film, a documentary, with interviews, nice shots of the lake, and it also used an underwater camera to shoot scenes hundreds of meters below the surface. Miguel Angel Rossi directed it, and it is really interesting.

Rossi has lived in Bariloche for the past 35 years, and was always interested in the Nahuelito. He tells about an incident involving an unusual sighting: (source)

Giant Aquatic Tortoise or Turtle

"Many years ago, when his daughters were young, Rossi had a strange experience: he saw something moving on a beach near the lake, and as he got closer, he saw it was an enormous aquatic turtle with a long neck. He turned it over, and the animal disappeared beneath the water once more. This led him to think that perhaps the Nahuelito could, in fact, be a turtle of extraordinary size."

His research led not only to reports on Nahuelito, but also to strange lights sighted under and above the lake, and strange shipwrecks.

He explored different theories about Nahuelito, from the "radioactive" one (involving the Atomic Energy research center on isla Huemul Island (1948-52) (see my 2010 post on this theory), to the "geologic" one, which attributes the sightings to degassing from faults in the lake's bed (See my 2010 post on this theory).

Strange Fish

The movie mentions "strange fish" that were introduced into the lake over 100 years ago. During the filming of the movie, they got images of some animals that are now being investigated. There are three species found in the lake that had not been officially recognized. "In addition to sightings of aquatic fauna species, there are concurrent accounts of experiences that are difficult to explain, many of them recorded. I believe that over time all of this will be revealed. And I hope that in a few years there will be many important productions investigating the lake's issues in all its forms."

Below is a picture with Rossi (left) on a boat in Lake Nahuel Huapi, while shooting the movie.

The Long Necked Tortoise

Rossi says that many people contacted him after the movie was released, and he is researching different theories. The tortoise is "...one of the ones that resonates most with me. After the film's release, a family story appeared that revives a theory I'd thought was dismissed. About eight years ago, this family experienced something that hadn't happened in 70 years. It intrigues me greatly because it's directly related to what Jarred Jones and others saw in the early 20th century: a long-necked animal. I had associated it with that turtle I saw years ago, but biologists tell me there are no turtles in the lake."

I must admit that I had never considered aquatic tortoises as a possible explanation for Nahuelito. I understood there were none in the Patagonian waters. There is a land tortoise in Patagonia, but now I have learned that there are freshwater tortoises in Argentina (see this paper) there are Phrynops hilarii, Acanthochelys spixii and Acanthochelys pallidipectoris in Mendoza province, just north of Patagonia. But the authors believe that they were introduced recently (pets released into nature). However, there is an ancient oral tradition of freshwater turtles in Las Heras and Lavalle Departments in that province in the early 1900s, both drained by the Mendoza River which formed part of the Desaguadero—Salado—Curacó rivers basin.

Notice the long neck of the Acanthochelys pallidipectoris (Chaco side-necked turtle) pictured below:

An Acanthochelys spixii or Black spine-necked swamp turtle:

And this is a Phrynops hilarii:

The Colorado River marks Patagonia’s northern border in Argentina, while the Desaguadero—Salado—Curacó system is a river which changes its name along its course, which is nearly 1,500 km long (932 mi.) Its northernmost sources are in the province of La Rioja, high in the Andes at an altitude of 5,500 m (18,000 ft.), and it flows in a north—south direction parallel to the Cordillera, receiving the input of many Andean rivers such as the Jáchal, Vinchinas, San Juan, Mendoza, Atuel, Tunuyán, and Diamante.

Water from many of these rivers is now diverted to irrigate the vineyards at the foot of the Andes in the Cuyo region provinces of La Rioja, Mendoza, and San Juan. This has led to a dramatic drop in the flow downstream along the Desaguadero River and the wetlands of Guanacache and Bañados del Atuel have dried up due to this cause, altering the environment and affecting the wildlife.

Until the early 1900s, the river carried plenty of water, and the western region of La Pampa was far more humid than it is nowadays. The Bañados del Atuel wetlands spanned 21,000 km² (8,100 sq.mi.) and had fifteen lakes. The westernmost branch of the river was known as Potrol stream, the Salado was its easternmost one. The wetlands drained into the saltwater lake of Urre Lauquen. Their outflow through the Curacó River (Mapuche for “stone water”) continues southward until it flows into the Colorado River at (38°50’S, 64°58’O). Its basin covers a surface area of 260,000 km2 (100,000 sq. mi.) The Colorado flows into the Atlantic.

It is feasible that the tortoises, if they lived in this basin, could have reached the Negro River, linked to the Neuquén and Limay rivers, and the Patagonian lake district. The Colorado and Negro run in more or less parallel courses with a minimum separation of 40 km (258 mi.) along a line linking the towns of Gobernador Duval and Chelforó. In other parts they can be up to 120 km or 74 mi apart. See the map below with the "Gap" that the tortoises would have to bridge between the Colorado and Negro rivers.

They are usually small, but in the U.S., the ke the Alligator Snapping Turtle (Macrochelys temminckii) which can weigh up to 176 pounds and reach a lenght of 40 inches (1 meter) (source). Not a monster, but big.

An obstacle is the temperature, the Andean lakes are cold, and these freshwater tortoises and turtles live in temperate, tropical and subtropical environments. A study involving turtles from Chaco, found that "The thermal breadth found in active individuals suggests that H.tectifera is a thermal generalist (eurythermal). Body temperatures of active individuals ranged between 10.1 °C and 25.7 °C (Mean = 18.58). Accordingly, records of individuals mating under water temperatures as low as 16.5 °C and 9 °C reflect the species capacity to perform activities within a wide temperature range.".

The temperature of Lake Nahuel Huapi (source) ranges from a minimum of 5.3°C in winter to a maximum of 19.5°C in Summer. The mean winter temperature for most of the lake is between 5.3 and 8°C, in summer it ranges from 15 to 18°C. They seem suitable for turtles. The lake also provides algae, crayfish, minnows, aquatic plants and insects, which make up the diet of these animals.

Further reading about the movie: Temporetti, Alonso. Bajo Superficie. Desde La Patagonia Difundiendo Saberes. Vol 19, N°34, 2022 ISSN (print)1668-8848 - ISSN (online) 2618-5385

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