A search has been launched for the assailants.
Wildlife officials said that a 20-month-old rare Indus dolphin swam into the Kirthar canal Monday afternoon, where some unidentified villagers shot it dead and fled.
Thereafter, the police were called to the scene. Local police have launched a probe into the matter.
"The carcass of the dolphin was first spotted by local irrigation staff," said Sindh Wildlife Department head Javed Ahmed Mahar.
"The villagers shot it dead before the rescue team could reach the area," he added.
As the name suggests, the Indus dolphin is primarily found in River Indus. Mahar explained that the dolphin made its way into Balochistan through the Kirthar Canal, which is linked to the Sukkur Barrage.
He added that the Sindh Wildlife Department was assisting local police in their probe.
Hurting or hunting the endangered blind Indus dolphin - one of the rarest mammals in the world - is punishable under the law. Last year a man in Sukkur had axed a dolphin to death that had been caught in a net. The man was sentenced to five years in prison and fined Rs250,000.
The Sindh Wildlife Protection and Preservation Act 2020, says that hunting and killing any endangered species is a cognizable offence.
According to the last survey, which was held in 2019, there were as many as 1,419 dolphins between the Guddu and Sukkur barrages. The area in which they were counted is called the Indus Dolphin Reserves.