An extensive algae bloom along Israel’s Mediterranean coastline in late August led to the closure of five out of six of the country’s coastal desalination plants, significantly disrupting drinking water supplies for both Israel and Gaza. The plants, which provide over 80 percent of Israel’s potable water, experienced clogged intake pipes caused by the bloom, prompting emergency responses from Israeli authorities.

Mekorot, Israel’s national water company, reported that as of early September, only one desalination facility was operating at full capacity, while others remained closed or worked at reduced output. The ongoing disruption persisted into its ninth day by September 7, with two plants still shut and three operating below normal levels. Private desalination facilities have partially resumed activity but have yet to reach full capacity.

In response to the shortage, Israeli officials imposed water use restrictions, increased withdrawals from reservoirs and the Sea of Galilee, and limited agricultural water allocations, aiming to stabilize the supply situation.

Scientific analysis indicates the algae bloom likely originated near Egypt’s Nile Delta, from where Mediterranean currents carried it north along the Israeli coast. Edo Bar-Zeev, an associate professor specializing in water research at Ben-Gurion University of the Negev, described the bloom as unprecedented in scale during his two decades of coastal monitoring. He estimated the algae extended over at least 12 kilometers.

Environmental specialists have pointed to untreated sewage from Gaza as a contributing factor exacerbating the nutrient-rich conditions favoring algae growth. Gaza’s wastewater infrastructure has suffered extensive damage amid ongoing conflict, with its six treatment plants reportedly damaged or destroyed in the recent war. Consequently, untreated sewage has flowed into the Mediterranean for months, further polluting the coastal waters.

The Israeli nonprofit Zalul Environmental Association analyzed satellite imagery and concluded that pollution fueling the bloom emanated from both Gaza and the Nile Delta region.

For residents of Gaza, however, the water crisis predates the algae event and is deeply tied to the destruction of local water and sewage systems amid warfare, as well as Israeli restrictions on supply and movement. Maysa Yousef, a mother and artist living in central Gaza, described early observations of algae forming inside water bottles filled with Mekorot-supplied water, which is piped into Gaza through transmission networks.

"I told my husband, ‘The water coming to us from Israel is contaminated. It is not clean,’" Yousef said, recalling her husband's initial disbelief given the water’s origin from Mekorot, which desalinate and treat the supply. Yet, the visible presence of algae within the bottled water confirmed the problem.

Following the announcement of plant closures in Israel, Mekorot reportedly cut water deliveries to Gaza. Given the extensive damage to Gaza’s own water infrastructure, many families had relied on this supply as one of the few sources nearing drinking-water standards, despite complaints about taste and quality.

Residents across Gaza also shared similar reports on social media citing algae and even small worms in their water. The incident has underscored the vulnerability of the shared water systems between Israel and Gaza amid environmental degradation and the ongoing humanitarian challenges in the region.