A striking natural spectacle has appeared along Vietnam’s western coast: a razor-clear line where blue seawater meets a reddish-brown band stretching for tens of kilometers.
The phenomenon has been visible for weeks near Da Bac, Tran Van Thoi and Khanh Hung communes in Ca Mau Province.
Nguyen Canh Hanh, vice chairman of the Da Bac People’s Committee, says it forms when heavy seasonal rains send large volumes of freshwater from inland fields rushing into the sea.
The seawater splits into two distinct colors in Ca Mau, southern Vietnam, December 2025. Video obtained by Read
As farmers drain their paddies during rice-sowing season, irrigation gates open simultaneously, pushing the lighter, tannin-rich freshwater outward and forcing saltwater farther from shore.
The two layers don’t mix right away. Instead they create a long, visible boundary: blue on one side, rusty red on the other thanks to the acidic soils and sediment flowing from the U Minh Ha lowlands.
Authorities emphasize this is a natural, temporary event rather than pollution, and it typically fades by the end of the month. But for now, the coastline is drawing attention for its dramatic, two-colored streak.
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