As soon as a large shark was spotted in a canal in Busan - a bustling shipping hub and beach city on South Korea's south-eastern tip - marine biologist Kim Hyun-woo was drafted in to rescue it.

He got the call in mid-September, on his way home from a business trip tracking shoals of mackerel to aid fishing vessels. Despite being one of the country's leading shark experts, he never thought he'd be asked by the coastguard to actually save one.

South Korea is no stranger to sharks but one this size, in a shallow, concrete canal right by the world's seventh busiest port, was unheard of - until now.

With an excited crowd already gathering at the waterfront, his team from the National Institute of Fisheries Science had to move fast. The first task was to determine the species.

Some sharks are more dangerous than others. The star of the 1975 blockbuster Jaws, the great white shark, is known to attack and kill humans.

The specimen in Busan was found to be a female dusky shark, a species linked only to two deadly attacks. Still, Kim feared someone in the crowd might jump or fall into the canal. The shark had to return to sea.

A small coastguard ship made an initial attempt using an electrical deterrence device, which generates a weak current that sharks avoid.

They're usually used after sightings near popular beaches. But after five hours, officials determined this particular shark was too large and fast for the device. Kim changed tack, deciding instead to wait for the shark to let herself out. But that did not happen.

As authorities looked for ways to guide her out of the canal, the stranded creature went viral.

Just hours after she appeared, the council had sent everyone in the city an emergency text alert, urging pedestrians and residents to "exercise caution for their safety".

People rarely visited the park along the canal but because of the message, the place was soon brimming with people eager to spot the shark.

Adoring fans named her Bukangi, from "buk hang", the Korean name of the nearby harbour. Within days, a business trademarked it and Bukangi pins, plushies and T-shirts began selling online. City authorities joined in, livestreaming the shark and making her their official mascot.

A banner was hung at the entrance of the canal, asking the public to sign a petition "on behalf of Bukangi" to demand the national government's support for the construction of a new 30,000-seater baseball stadium by the canal.

Shark spotting became a team effort among locals and visitors. The unspoken rule was that children were given the front row, and whoever saw Bukangi had to point her out to newer arrivals.

Some self-appointed defenders even patrolled the canal at night to make sure no-one was shining torches or lasers at Bukangi. More than 1.6 million visitors ultimately flocked to the canal.

The local mayor said the shark brought "the kind of publicity even billions of dollars cannot buy" to the port.

"It's really rare these days for people to come together," said Kim Joo-eun, who came to see the shark with her two nieces. "I feel that Bukangi brought us all together, cheering for her… It's a lot of fun." But officials couldn't leave Bukangi in the canal.

As September drew to an end, she hadn't been seen feeding for days and was spotted with bloody abrasions on her snout from bumping into the concrete walls.

Prominent marine biology professor Choi Yoon told local media that experts were particularly worried about a "critical" injury around the shark's eye.

At the end of September, Kim's team mounted another rescue attempt. The marine biologist looked back to a 2004 incident in Massachusetts, when water jets were used to drive a great white shark away from a shallow pond. But when the team tried this on Bukangi, she kept circling back.

On 2 October, they decided to install a net spanning the width of the canal to stop her from returning. She managed to swim around the net and was back within hours.

At this point, Kim started thinking the shark might have problems with her snout's electromagnetic sensors, which she uses for navigation. Or she might have become confused by the loud noises emitted by ships in the harbour.

The reason Bukangi was even in the canal may be a sign of warming seas, the oceans ministry suggests.

It believes she may have followed plentiful fish to warmer waters. Some 50 large sharks were recorded off South Korea's east coast in the first half of the year; four times as many as last year.

With each failed attempt some of Bukangi's newfound fans began demanding she be left in peace.

On Thursday, several showed up with placards and shouted "leave Bukangi alone" and "remove the net". When a security guard told them to stop, one man cried: "I love you, Bukangi!"

"I am obsessed with her," said Jeong Yo-won, a woman in her 40s. She called the shark a "source of hope and joy" and insisted, "I don't think we should evict her mercilessly like this." Others thought it was time for her to return home.

"I would stare at her for hours because I was so enamoured by her," a woman said after sighting the shark on her third attempt. "I hope Bukangi would stay, but I prefer that she lives a long and healthy life." People joked the council should "make an official ID for Bukangi and give a pension", Shin Seungmin said.

"She brought so much fun with her. But she should go and live her normal shark life." Staying in the canal would seriously jeopardise Bukangi because of falling autumn temperatures, Kim explains. Usually this prompts sharks to migrate to warmer waters further south.

"This canal is far from something we can call a habitat," he adds. "A wild animal cannot stay in a space made strictly for humans." Eventually, as public scrutiny grew, the oceans ministry took over the rescue operation from the fisheries institute. Around 40 personnel, including divers from Busan's aquarium, were mobilised. A vet was on standby, along with an ambulance in case the divers were attacked by Bukangi.

On Wednesday divers installed two layers of nets, and Bukangi was successfully herded out of the narrow canal into open water. But overnight, she swam back into the canal, diving under the outer net. This left her trapped between the two layers.

Then on thursday, rescuers removed the outer layer, and Bukangi was seen swimming further and further towards open sea. Although she did occasionally circle back, the rescue operation had ended.

There have been no sightings of Bukangi in the last few days, which experts say is a positive sign. Prof Choi believes she may be adjusting to wider, deeper waters. She is unlikely to have travelled far, he adds, and could reappear over the coming week.

But he is also worried about any injuries she may have sustained. Trapped in the canal, it "kept scraping against [the walls], stripping the skin off its snout and even its pectoral fins", he told local media.

For now, South Korea is holding its breath, hoping Bukangi can find her way back to her home - the open sea.