Officials evacuated Fiesta Island in the Mission Bay area on Saturday evening after tourists spotted an explosive device in the sand, according to San Diego police.
Police reported the discovery around 3:25 p.m. Soon after, officials ordered everyone evacuate the island.
From there, the San Diego Fire-Rescue Department's Metro Arson Strike Team used a robot to take pictures of the 60 millimeter mortar. Those pictures were sent to a military bomb squad, which soon arrived to take over the investigation.
"There was enough concern in this incident that they did feel that there was a danger and that it was highly probable that it was a live, high explosive round," said Lt. Paul Rorrison with the San Diego Police Department.
Visitors who parked on the island were stranded on the mainland for hours while crews investigated.
That's exactly what happened to Chuck and Rhonda Martin, who had to leave their truck on Fiesta Island as they moved to safety with their bikes.
This was the last thing they expected, and they said it's the last time they'll park there.
"I'm cold, hungry, tired and I want my truck," said Chuck.
After a couple of hours, people were let back onto the island, and no one was injured.
The military bomb squad took the mortar to a bunker, where they will examine and destroy it.