Red tide spreads to southern coast as fish farms brace for double blow

Anxiety is mounting among fish farmers along South Korea's southern coast as red tide shows signs of spreading, compounding ongoing damage from high water temperatures driven by a heat wave. The government raised its red tide crisis alert to the Caution level after preliminary red tide advisories were issued for waters off eastern South Jeolla Province and western South Gyeongsang Province.

The Ministry of Oceans and Fisheries said it issued the Caution-level red tide crisis alert effective 6 p.m. Monday, after the National Institute of Fisheries Science issued preliminary red tide advisories at 4 p.m. the same day for two sea zones — waters off eastern South Jeolla Province and western South Gyeongsang Province.

The red tide crisis alert system rises through four levels: Attention, Caution, Alert and Serious. A Caution alert is triggered when preliminary advisories cover two or more sea zones; the level rises to Alert when full advisories cover two or more zones, and to Serious when red tide warnings cover two or more zones.

A preliminary red tide advisory is issued when the concentration of harmful red tide organisms exceeds 10 individuals per milliliter. The threshold rises to 100 per milliliter for a full advisory and 1,000 per milliliter for a warning.

Water temperature is the key variable driving this outbreak. The National Institute of Fisheries Science said Cochlodinium populations are growing along the coasts of eastern South Jeolla Province and western South Gyeongsang Province, where water temperatures have remained between 24 and 27 degrees Celsius — ideal conditions for the organism's growth. The institute warned that if similar temperatures persist and competing organisms decline, populations could increase further, particularly in the Bodol Sea off Yeosu.

Cochlodinium is a harmful red tide organism that attaches to the gills of farmed fish, obstructing respiration and, in severe cases, causing death by asphyxiation. Concerns are growing that fish farms could suffer serious losses if red tide strikes while fish are already weakened by high water temperatures.

The ministry drew up a comprehensive 2026 high-water-temperature and red tide response plan in June, which included supplying yellow clay and other control equipment and conducting joint public-private response drills. Following the Caution alert, the ministry plans to activate its integrated operations center and step up red tide surveillance, spread-trend analysis and situation reporting.

The ministry urged fish farmers to pursue early harvests, adjust feed supply, reduce stocking density and conduct advance checks on control equipment.

Oceans and Fisheries Minister Hwang Jong-woo said the ministry is concerned about additional damage from rising harmful red tide organisms on top of fish farm losses already being caused by high water temperatures from the heat wave. "We will conduct advance inspections of fish farms together with local governments and respond in line with how the red tide spreads," he said.