At least 26 dolphins died or had to be put down after becoming stranded in shallow water in the Percuil River near Falmouth on Monday, the largest number for 25 years in the U.K.
A spokesman for the British Divers Marine Life Rescue (BDMLR) said the animals had no food in their stomachs, indicating that they could have panicked and headed for shore. He said that there was no "evidence" they were feeding prior to death.
The Royal Navy has confirmed it was conducting a live firing exercise with submarines and warships several hours before the stranding. The exercise also included shooting practice.
"It is considered extremely unlikely that this operation could have affected the mammals in any way," a navy spokesman said. "We take our environmental responsibilities very seriously and always carry out an environmental impact assessment before putting energy in the water."
"I have never heard anything like this, certainly not in the U.K. and possibly not anywhere," the British Divers Marine Life Rescue (BDMLR) chief Alan Knight earlier said. "My own personal conclusion is that there was some sort of disturbance that caused the animals to panic."
Other theories for the stranding are that the dolphins were stranded after fleeing a predator. Dolphins can become stranded for a number of other reasons, such as injury, disease, disorientation or extreme weather conditions.