Bamseom was "reborn" as the river deposited sediment and sand, expanding its area by about 4,400 sq m a year. It's now about 3km around its shores and, at about 280,000 sq m, is half the size of Singapore's Coney Island and six times larger than its original area.

Now covered with thick vegetation, the uninhabited island draws so many species of birds and fish that it was designated an "Ecosystem Reserve" in 1999 by the Seoul city government.

It was recognised as an internationally important wetland by the Ramsar Convention in 2012, three years after it featured in the award- winning Korean movie Castaway On The Moon, starring Jung Jae Yeong as a man stranded after a failed suicide attempt.

Bamseom is now maintained by the Hangang Business Centre and ecologists are studying birds such as the white-tailed eagle and brown hawk owl that have migrated to the island, said ecologist Lee Ho Young.

"There is no human touch to Bamseom. We are keeping it natural as an ecological park, and for research and education purposes," he said.

The varieties of birds, fish and plants found on the island have grown over the years. As of 2012, there were 49 kinds of birds, 39 species of fish and 138 types of rare plants recorded, said Dr Lee.

On a media trip organised by the Seoul Metropolitan Government, hundreds of cormorants took flight, a far cry from the few dozen that lived there a decade ago. Dr Lee said there are about 500 on the island now.

Bamseom is closed to the public, but every September, during the Chuseok autumn festival holidays, former residents are allowed to revisit the island for a homecoming celebration.

Mr Yoo, a security guard, joins in with a bottle of makgeolli (Korean rice wine) at a spot near where he used to live. His grandparents were born on Bamseom, he said.

People started moving there during the Joseon dynasty (1392-1910) and they made a living building ships, fishing and farming, according to official records.

During his time, Mr Yoo said 10 of the 64 families living on the island worked in shipbuilding, while the rest were farmers or fishermen. His family had a peanut farm but Mr Yoo worked at an energy company located on the mainland.

With no electricity or water supply on the island, residents had to drink water from the river and use candles or kerosene lamps at night.

But the inconvenience was a small price to pay for the lifestyle they enjoyed. "Life was so relaxing then. The scenery was great and we had the best sandy white beaches that would draw lots of visitors during summer," he recalled.

The 64 households were relocated to the slopes of Mount Wawoo in the Mapo district in western Seoul. Mr Yoo said they received total compensation worth 15.7 million won (S$19,000) and were able to build their own houses on government-assigned land.

About 50 residents still keep in touch regularly, as part of a Bamseom residents' committee headed by Mr Yoo. Every one or two months, some gather at Bamseom Temple, which was also relocated to Mount Wawoo.

The residents, mostly in their 70s and 80s, help to maintain the temple that was built around the time the Joseon dynasty was founded. It is registered as a heritage site and receives government funding for maintenance.

The committee organises the annual homecoming festival to Bamseom and keeps a community history record called Bugundanggut.

University of Seoul researcher Kwon Hyeok Hee, who did a PhD on Bamseom residents in 2013, said they have managed to keep their culture alive even after leaving the island.

Mr Yoo hopes to do more for the island home he dearly misses, but laments that time is running out, given the ages of the people and that not many want to participate.

He hopes to launch a website to record Bamseom's history and start a boat tour for students.

"My final goal is to start a private organisation to take care of Bamseom," he said. "I miss my hometown, and I feel someone needs to take care of the island."

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