U.S. Navy and Japanese officials are investigating the cause of an oil spill Sunday in Yokosuka Bay.

The spill of more than 13,400 gallons of bilge water containing ship oil was discovered around 6:30 a.m. Sunday as the fuel was being transferred from the USS Kitty Hawk to a barge at Yokosuka Naval Base, Japan.

According to Yokosuka Naval Base spokesman Mike Chase, Japanese officials were notified of the spill immediately and the cleanup was nearly complete by Wednesday.

But Yokosuka city officials say they weren’t notified until Tuesday, more than a day after about 9,000 gallons of oily water had been recovered.

“Whereever the fault may be, the city needs to be notified earlier since it manages ports,” said the city’s base liaison, Nagatoshi Esashi, adding the city was notified by Yokohama Facilities Administration Bureau.

The city plans to suggest the Navy notify the city directly and promptly.

Leaking oil was discovered around 6:30 a.m. Sunday, Chase said. Protective booms were already in place around the ship and prevented the oil sheen from spreading.

The Navy used three oil skimmers and oil-absorbent pads to collect the oily water, officials said.

Investigators believe the spill may have been caused by a failed pump circuit-breaker aboard the barge, officials said. With the breaker shorted out, oil spilled into the bay.

A Japanese contract company owns the barge, Chase said.

Juliana Gittler contributed to this report.