An 8-meter-long whale was spotted near the mouth of the Yodo River in Osaka on Monday, a rare sighting of the large mammal in Osaka Bay, according to the coast guard.

A truck driver on an expressway parking area near the river mouth reported finding a whale-looking animal spouting shortly after 7:30 a.m. A coast guard vessel was dispatched to the site and monitored the whale to keep it from going further upstream.

Photo taken from a Kyodo News helicopter shows a whale found close to the mouth of the Yodo River in Osaka on Jan. 9, 2023. (Kyodo)

The coast guard also warned ships navigating the area to watch out for the animal.

"It could be a young sperm whale living in the Pacific Ocean that strayed from its herd. It may be frail because it looked as though it was just floating," Tsutomu Tamura of the Tokyo-based Institute of Cetacean Research said in a statement.

Photo shows a whale spotted near the mouth of the Yodo River in Osaka on Jan. 9, 2023. (Photo courtesy of the Osaka Coast Guard Office) (Kyodo)

Osaka Bay is largely enclosed by Awaji Island, which leaves two narrow passages north and south. The southern opening leads to the Pacific.

Photo taken from a Kyodo News helicopter shows a whale found close to the mouth of the Yodo River in Osaka on Jan. 9, 2023. (Kyodo)