There are some pretty humongous fish swimming around Southeast Asia’s rivers. In fact, there are two very different species that are both contenders for the region's largest freshwater fish: the Mekong giant catfish and the giant stingray.

The biggest Mekong giant catfish ever caught was almost 3 meters in length (9 ft) and weighed a mammoth 300 kilograms (650 lb), leading it to be crowned one of the largest freshwater fish ever recorded (sturgeons, however, seem to be at the top of the list). But this beast could have a contender on its hands as scientists in Thailand have just reeled in a whopper stingray that could be as much as 60 kilograms, or 150 pounds, heavier.

As reported by National Geographic, the animal was caught in an area of Thailand’s Mae Klong River, around an hour from the capital Bangkok. Veterinarian Nantarika Chansue, one of the team that helped catch and measure the ray, told the magazine that the animal was 4.3 meters (14 ft) in length and 2.4 meters (7.9 ft) in width, weighing an estimated 318 to 363 kilograms (700 to 800 lb).

Unfortunately, the team was not able to weigh the animal to get an accurate number because, as pointed out by National Geographic fellow Zeb Hogan, this species is so big and awkward it is difficult to weigh them without causing injury. Regardless, it is no doubt a remarkable animal and certainly one of the largest freshwater fish documented so far.

This was not actually the first time that scientists encountered this particular animal: It was first caught back in 2009 as part of a National Geographic expedition that aimed to identify and protect the world’s largest freshwater fish. The ray was caught and released on January 28 of that year, but before letting the animal go, scientists attached an electronic tag and performed a brief examination, which revealed that she was pregnant. Encouragingly, after giving the animal an ultrasound scan this time around, scientists found that she was once again pregnant with two fetuses. That was good news, Hogan says, because it suggests this area is a nursery ground for these animals.

By tagging these animals and checking up on them every few years, scientists can further their understanding of their growth rates and infer their approximate lifespan, which is currently unknown. This particular ray was actually a foot longer back in 2009, which the team thinks could be the result of an accident or perhaps a scrap with a male, both of which could have shortened her tail.

Scientists are interested in these behemoths because both Thailand’s subpopulation of giant freshwater stingrays and the Mekong giant catfish are listed as critically endangered on the IUCN Red List. While both are threatened by habitat destruction and alteration, such as pollution and dams, the latter also faces overfishing. Hopefully, with continued conservation efforts, populations of these animals can slowly begin to recover.