Intense Rainfall Turns Hormuz Island Coastal Waters Crimson Due to Iron Oxide Runoff

Coastal waters surrounding Iran's Hormuz Island in the Persian Gulf exhibited a vivid reddening on Tuesday, December 17, 2025, following a period of intense, localized rainfall. This natural occurrence, documented widely on social media, was scientifically attributed to the erosion of the island's distinct, mineral-rich geology. The striking discoloration resulted from an unusually heavy downpour, reportedly depositing nearly 100 millimeters, or four inches, of rain overnight, a volume nearly five times the region's typical monthly average.

This rapid precipitation led to significant surface runoff, washing iron-rich soil, known locally as *golak*, from the island's cliffs into the sea. Scientists confirmed that the crimson hue is caused by a high concentration of iron oxide, specifically the mineral hematite, present in the island's volcanic soil—the same compound responsible for the reddish surface of Mars. Hormuz Island, recognized as the "Rainbow Island of the Persian Gulf," possesses a unique geological profile as a salt dome embedded with layers of clay, carbonates, shale, and volcanic rocks containing over 70 different minerals.

The island's existing iron oxide deposits already create permanent red beaches, such as the *Sahel Sorkh*. However, the exceptional intensity of the December 17 rainfall mobilized these fine mineral particles through erosion channels, causing colored streams to surge toward the coast and temporarily dye the shallow seawater. Experts concluded that the event is entirely temporary and poses no known threat to human health or marine ecosystems, distinguishing it from a biological event like a red tide.

This visual event unfolded against the backdrop of a severe national environmental crisis, as Iran in 2025 was contending with one of its worst droughts in five decades. Data from the Ministry of Energy indicated critically low reservoir levels supplying Tehran, with some major dams operating at single-digit capacity; preceding months saw the capital's water reserves reduced to approximately 14 percent of capacity. While the local rain was locally celebrated, officials noted that such sporadic events do not alleviate the structural water deficit facing the nation, which is attributed to long-term water mismanagement alongside climate change.

The rapid precipitation also presented infrastructure challenges, as authorities in Hormozgan province closed roads due to localized flooding. Culturally, the iron oxide, or *golak*, holds traditional significance, having been used by local residents for centuries as a natural pigment, for cosmetics, and as a spice in local cuisine. The geological composition of Hormuz Island continues to be a subject of fascination for geologists and artists utilizing the mineral deposits for creating expansive sand carpets.

The scientific consensus affirms that the spectacular red water is a temporary chemical reaction between water and hematite, not a biological phenomenon. The event underscores the complex interplay between localized, intense weather patterns and the underlying environmental vulnerabilities of the region.