The sea around Koh Larn has turned green, surprising tourists. This is suspected to be a "plankton bloom" following heavy rain in Pattaya that caused a large amount of freshwater to flow into the sea.
On 30 September 2026, reporters reported the situation around Koh Larn, Pattaya City, Chonburi Province, after some areas of the sea were observed to have a green color different from normal, surprising tourists visiting for leisure.
Initially, this condition aligns with the sea color change phenomenon known as "plankton bloom," which can naturally occur, especially during the rainy season.
This situation arose after Pattaya and nearby areas experienced heavy rain, strong winds, and unstable weather recently, resulting in increased freshwater, nutrients, and sediments flowing from land into the sea. These factors promote rapid plankton growth, changing the sea color from normal to green or other colors depending on plankton species and density.
Information from the Department of Marine and Coastal Resources states that the sea color change occurs when plankton multiply rapidly. Coastal nutrient levels, currents, temperature, and weather conditions all contribute. During the rainy season, water flowing from land carries nutrients into coastal areas, increasing their concentration.
The "plankton bloom" phenomenon typically follows heavy rainfall and freshwater inflow into the sea, after which the water gradually returns to its normal condition.