A cause of death may never be known for the dolphin that washed up on a Baldwin County beach Monday, the Alabama Marine Mammal Stranding Network said Tuesday.

A five-hour necropsy was performed at the Dauphin Island Sea Lab on the bottlenose dolphin found dead Monday on North Beach in Fairhope. Researchers at the network took hundreds of samples to determine the dolphin’s cause of death.

But the dolphin’s level of decomposition means a cause of death “may not be able to be determined,” the network said Tuesday.

Still, the necropsy’s samples are “critical to ongoing research about the health and population of Alabama dolphins,” the network said.

The dolphin had signs of “prolonged freshwater exposure,” including skin lesions and algae matted on its body.

It’s unclear how long dolphins can survive in freshwater, but the Sea Lab had a case of a stranded dolphin in Alabama that survived in similar conditions for more than 30 days in 2016.

The dolphin discovered dead Monday was underweight and dehydrated, the necropsy showed.

Results from diagnostic tests are expected to take weeks to months.

The dolphin is the 12th found stranded in Alabama since January and the 10th in Baldwin County.

Those numbers are typical for this time of year, according to the network.

Anyone who encounters a stranded, injured, or dead marine mammal is advised to not push the animal back into the water.

Instead, call 1-877-WHALE-HELP as soon as possible to be connected to a trained responder, the network advised.