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Jeju's beaches blanketed by drifting wireweed, as officials and volunteers try to clean up the problem

Published: 17 Feb. 2026, 18:12

Masses of Sargassum horneri, also called Asian wireweed, blanket Ihoteu Beach and nearby coastal areas in Jeju City on the afternoon of Jan. 9. [JOONGANG ILBO]

On a crisp morning in early January, Ihoteu Beach on Jeju Island was covered with a long dark-red belt that stretched between the blue sea and white sand. Clumps of tangled Asian wireweed at the edges of the waves extended out more than 100 meters, blanketing the shoreline. Piles layered atop one another rose up to knee-high levels. Up close, a pungent, fishy odor filled the air.

Entwined within the seaweed were discarded ropes, Styrofoam, broken buoys and plastic containers. Kim, a Jeju resident who regularly walks barefoot along the shore for exercise, was among the beachgoers carefully navigating between the debris. “We usually see this seaweed in spring, but this year it appeared as early as January. As the weather warms, the smell is stronger than in previous years, making it hard to walk.”

By afternoon, around 10 members of a marine environmental protection team were working with rakes to remove fishing gear and debris caught among the seaweed. “Even after we clear it away, a single high tide brings it back,” said a crew member surnamed Kim. “The seaweed and trash burrow into the sand, so we’ll likely need heavy equipment like excavators.”

Nearby pebble beaches showed similar conditions: Fishing gear waste and masses of seaweed lined the rocky shoreline.

Response team launched early over influx from China

A Jeju marine environment worker carries out cleanup operations on masses of Sargassum horneri, or Asian wireweed, covering Ihoteu Beach and nearby coastal areas in Jeju City on the afternoon of Jan. 9. [JOONGANG ILBO]

As large inflows of Asian wireweed ( Sargassum horneri) began appearing along the island’s coastlines, the Jeju provincial government formed a response task force last month. The seaweed typically washes ashore between March and June, but this year it began arriving as early as January.
Experts trace the origin of the washed-up seaweed to China’s southern coast. In 2015, the National Institute of Fisheries Science analyzed the genetics of specimens that had drifted ashore and found that they matched populations from the East China Sea. Around the same time, China was transplanting large amounts of Sargassum horneri as part of marine reforestation and ecological restoration projects tied to the development of its marine economy.

Once detached by waves and wind, the seaweed drifts northward along the Kuroshio current. It is later carried by the Tsushima warm current and westerly winds, eventually reaching southwestern Korean waters and Jeju.

A plastic bottle bearing Chinese-language markings lies tangled among the masses of Sargassum horneri, or Asian wireweed, covering Ihoteu Beach and nearby coastal areas in Jeju on Jan. 9. [JOONGANG ILBO]

The sharp increase in seaweed arrivals along Jeju’s coast since 2015 lends weight to this explanation. The repeated discovery of debris bearing Chinese-language markings among the washed-up masses further strengthens the link.

More recently, rising sea temperatures in the Yellow Sea have expanded suitable habitats farther north, with some populations from those waters also drifting toward Korea’s coastline.

Inedible, unlike local seaweed

Masses of Sargassum horneri cover Ihoteu Beach and nearby coastal areas in Jeju City on the afternoon of Jan. 9. [JOONGANG ILBO]

Over the past five years, 11,611 tons of Asian wireweed have been collected in Jeju. The largest amount was recorded in 2021 at 9,756 tons, followed by 412 tons in 2022 and 201 tons in 2023. The volume rose again to 921 tons in 2024, with 321 tons collected so far in 2025. Annual totals vary depending on ocean currents, weather and water temperature.

The problem extends beyond spoiled scenery. Large floating mats of seaweed cling to aquaculture nets and facilities, disrupting fishing operations. When entangled in boat propellers, they pose risks to navigation and safety. Further unlike cham mojaban — edible seaweed used in Jeju’s traditional momguk soup —Asian wireweed is tough and unsuitable for consumption. Left unattended, it decomposes and produces an even stronger stench.

16.4 billion won allocated for marine cleanup

Discarded fishing gear and masses of Sargassum horneri blanket the coastline of Iho-dong in Jeju City on the afternoon of Jan. 9. [JOONGANG ILBO]

This year, Jeju plans to invest 16.4 billion won ($11.35 million) across 13 projects, including marine waste cleanup, environmental patrol programs and aquaculture site restoration. Some collected seaweed is repurposed as farm compost but large quantities are incinerated.

“We are closely monitoring changes in the timing and scale of inflows,” a Jeju government official told the JoongAng Ilbo. “Our goal is to minimize inconvenience to tourists and damage to local fisheries.”

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.
BY CHOI CHOONG-IL [[email protected]]