Microalgae bloom forces shutdown of most Israeli desalination plants

A miles-long microalgae bloom in the Mediterranean Sea caused five of Israel's six coastal desalination plants to shut down on Sunday, according to Mekorot, the national water company. The facilities, which together supply about 65% of the country's drinking water, have since resumed partial operations, but only one plant was running at full capacity by Thursday.

"An event of this kind has never occurred before in Israel … it was an extremely rare event," Mekorot spokesperson Lior Gutman said, adding that water shortages have not been reported in roughly 99% of cases.

Scientists identified the bloom as a rapid growth of microalgae, likely originating in the Nile Delta and carried northward by currents. Associate professor Edo Bar-Zeev of Ben-Gurion University, who has monitored coastal water for two decades, described the bloom as extending over a dozen miles, a scale he had not previously observed.

The algae and their by-products can foul the reverse-osmosis membranes used in desalination, reducing the plants' ability to treat water, explained Michael Christopher Low, director of the Middle East Center at the University of Utah. Similar disruptions have occurred elsewhere, such as the red-tide events that affected Gulf of Oman plants in 2008-2009.

To offset the loss, Mekorot activated water from the Sea of Galilee, groundwater wells and national reserves. Some municipalities imposed short-term restrictions on garden irrigation and pool filling, while farmers using potable water for irrigation faced the most significant limitations.

The bloom coincided with a summer period of peak water demand and followed a sea storm that increased water turbidity and raised sea temperatures above 30 °C, creating a “very unusual combination of factors,” Mekorot said.

Experts warned that such events may become more frequent as climate change drives higher ocean temperatures, altered currents and stronger storms that introduce nutrients and pollutants conducive to algae growth. They also highlighted broader vulnerabilities of desalination systems to natural, geopolitical and cyber threats.