TEMPO.CO, Jakarta - Lake Singkarak in West Sumatra, the second-largest lake on the island, has captivated both local communities and the online world due to its unusually clear appearance. Contrary to expectations, which anticipated a muddy-brown mixture from the recent fatal floods and landslide materials, the lake now appears strikingly clean.
Several videos showcasing the shift in Lake Singkarak's water color have gone viral. One of the uploaders, Nurul Hidayati, a university student whose campus is close to the lake, which is famous for its endemic Bilih fish, did not want to miss capturing the social media phenomenon, particularly on TikTok.
"The water does have a greenish color, but when seen directly, it appears much brighter than before," Nurul told Tempo on Thursday, December 4, 2025.
Nurul visited the outlet of Lake Singkarak, specifically along the Ombilin River in Tanah Datar, on December 1, 2025. She noted that after she finished filming the clear, green water, the color returned to a brownish hue later that afternoon.
The Clearing Effect of Junjung Sirih Karst
Ade Edward, a Geologist from West Sumatra, explained that the color change in Lake Singkarak's water is caused by limestone solution being carried into the lake by river flow. Ade stressed that this phenomenon is not new and occurs frequently.
"It is similar to the process used in purifying swimming pools or by regional drinking water companies, which utilize limestone solutions," Ade told Tempo.
According to him, the Lake Singkarak area is located within the Median Graben, a downward rift in the actively shifting Sumatran Great Fault. The geological structures controlling this region, such as the Paninggahan fault and the Muara Pingai fault, influence the position and surface exposure of limestone rocks.
This limestone, or Junjung Sirih karst, makes the water flowing into the lake rich in calcium carbonate. Ade continued that calcium carbonate naturally binds and settles sediments and particles that cause the water to become turbid.
"Through this process, the pollutants causing the turbid water are carried to the bottom of the lake, while the surface water becomes clear," he explained. Therefore, the more water that flows through the karst area toward the lake, the clearer the lake surface will appear.
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