The U.S. Coast Guard is not sure how to salvage a former Navy tugboat that has been leaking oil since it sank in shallow waters in the Port of Richmond on Sunday.

The sunken vessel continued to leak fuel Friday, although the flow of oil is slowing. According to the California Department of Fish and Game, no birds or mammals have been harmed by the spill.

The Coast Guard does not know how much oil remains in the tanks of the Tiger, formerly called the USS Quapaw. But officials say it can hold 50,000 gallons of fuel — almost as much as the amount that the Cosco Busan spilled after it struck the Bay Bridge in 2007.

“Without firm schematics of the vessel layout and the tanks and all that, it’s hard for us to get a figure on the amount of [fuel] that’s in there,” said Coast Guard Lt. John Livingston.

Click through the slideshow for more information about the ship's history and the spill:

• 
• 
• 
• 
• 
• 

Correction: A previous version of this slideshow misstated the year when the USS Quapaw, now named Tiger, was built. It was constructed in 1942, not 1952.