Whenever a large number of animals are found deceased, it’s cause for concern and investigation. But when those animals are endangered giant stingray the size of cars, it’s especially alarming.

Last week around 70 giant stingrays, some as big as eight feet across and 14 feet long, were found on a stretch of the Mae Klong River in Thailand. Wildlife officials in the country were immediately seeking a cause to the die-off, but not sure yet.

Measurements showed a higher acidity level in the waters, but that has not yet been confirmed as the cause, according to National Geographic. Others suspect the cause could be raised levels of pollution in the waters as a result of nearby factories.

The rays, which can weigh up to 800 pounds, are not fished by anglers because they are not good to eat and are often too large to reel in. But they do get caught in fishing nets and are affected by dams and pollution.

Photo credit: Youtube