Nanaimo Port Authority responded with oil booms after a dive charter boat took on water and sank in Newcastle Channel Thursday.
The sunken vessel was reported by a passerby at about 7 p.m.
The 12-metre-long vessel turned on its side and sank while it was tied up at a marina on the 1200 block of Stewart Avenue.
Port authority crew deployed containment booms to prevent the spread of a small amount of gasoline and oil that had seeped from the craft.
David Mailloux, Nanaimo Port Authority spokesman, said the boat was pulled from the water and taken to Newcastle Marina for inspection, where it was discovered a leak was caused by a hole that formed where an engine mount connects to the hull.
No one was injured, no other property was damaged and the cause of the failure is being investigated.