Firefighters rescued eight people from an overloaded airboat Thursday after it struck a submerged piling in the Bay and started taking on water, authorities said.

No one was injured in the approximately 8:35 a.m. incident that left the group stranded about one mile south of the Dumbarton Bridge and 150 yards offshore. Because the tide was going out during the rescue the boat ending up coming to rest in some mud instead of sinking, Menlo Park Fire District Division Chief Frank Fraone said.

"They were very lucky," said Fraone. "There were no (life jackets) onboard and that's illegal."

He added the boat was also overloaded by at least two people, though he wasn't sure of its exact capacity.

The people were from an environmental group, the name of which wasn't immediately available, that were in the San Francisco Bay to identify and remove certain plants. Fraone had no further details.

While on the water they struck the submerged remains of a piling that was part of a railroad trestle that once crossed the Bay, but burned in the 1990s, Fraone said. Damage from the crash caused the boat to take on water, and prompted the group to call for help.

After firefighters took the people ashore, the stranded boat was drained and driven back to land.

Contact Joshua Melvin at 650-348-4335. Follow him at Twitter.com/melvinreport.