SEOUL, South Korea (AP) — South Korean officials on Wednesday struggled to free a huge gray shark that has been trapped for more than a month in a canal in the port city of Busan.

Officials used a floating platform to herd the 3-meter-long (9.8-foot) female dusky shark, nicknamed Bukangi after the Korean name for Busan’s North Port, through the narrow waterway for hours. But by evening, the animal remained at the mouth of the canal rather than swimming out to open sea.

The shark was first spotted in mid-September and became a major tourist attraction as it slowly circled the canal, its fins slicing through the water’s surface.

Busan officials, who made Bukangi a city mascot, said the shark attracted more than 1.6 million visitors to the canal. But they struggled for weeks to find a way to guide it back to the open sea.

Wednesday’s operation was the third attempt to free Bukangi, following failed efforts on Sept. 29 and Oct. 2 that involved boats spraying streams of water and nets placed across the narrow waterway. The shark avoided the boats and swam over the nets.

Experts have raised concerns about the shark’s condition, saying it had shown no signs of feeding during its monthlong stay in the canal and that falling water temperatures posed additional health risks.

Wednesday’s operation involved painstakingly maneuvering a large floating platform through the canal to drive the shark out. Workers stood on the platform and used oars to push Bukangi back whenever it approached. Dozens of other workers on both banks pulled ropes to drag the structure forward, as hundreds of onlookers lined the canal to watch the highly unusual rescue effort.

Workers managed to push the platform about a kilometer (0.6 miles) toward the mouth of the canal and placed additional netting in front of the structure to prevent the shark from swimming back in. Camera and drone footage showed the shark swimming near the platform and netting for hours, instead of swimming away to outer sea.

“During Bukangi’s 34 days in North Port, the shark became a friend to the entire country and a symbol of Busan, the nation’s maritime capital. It’s heartbreaking to say goodbye,” said Busan Mayor Chun Jae-soo in a Facebook posting. “We will do everything we can until the very end to ensure Bukangi’s safe return to nature.”