An unprecedented large-scale algal bloom along Israel’s Mediterranean coastline has forced the temporary shutdown of five out of the country’s six major seawater desalination facilities, triggering a fresh discussion over environmental vulnerabilities in the region and the multiple factors that may have sparked the historic event, according to regional and international media reports.
Desalination is the backbone of Israel’s drinking water supply, meeting more than 65 percent of the nation’s demand, with nearly all major desalination infrastructure sited along the Mediterranean coast. Lior Gutman, a spokesperson for Mekorot, Israel’s national water utility, confirmed the scale of the disruption, noting that an event of this magnitude has never been recorded in Israeli history. “An event of this kind has never occurred before in Israel … it was an extremely rare event,” Gutman stated. The affected plants include key facilities at Ashkelon, Ashdod, Palmachim, Sorek A, and Sorek B.
In response to the shutdowns, Israeli water officials moved quickly to stabilize the national water supply by drawing increased volumes from the Sea of Galilee, underground groundwater reserves, and existing storage reservoirs, while implementing limited restrictions on agricultural and public irrigation. Even as supplies remain stable for the moment, the crisis has pulled back the curtain on a critical fragility: Israel’s heavy reliance on desalination leaves it exposed to unexpected large-scale environmental disruptions.
Israeli news outlet Ynet first reported that one leading potential cause being examined by researchers is the massive volume of untreated sewage flowing into the Mediterranean from the Gaza Strip, where the local wastewater treatment infrastructure has sustained severe damage during the ongoing conflict. Palestinian and Israeli data indicates roughly 40,000 cubic meters of untreated wastewater enters the sea from Gaza every day. A number of leading Israeli environmental researchers have pointed to this nutrient-rich runoff as a key contributing factor.
Algal blooms require two core conditions to proliferate: warm water and high concentrations of nutrients such as phosphorus and nitrogen, explained Avner Gross, head of Ben-Gurion University’s Climate Change Laboratory. While satellite data has detected similar algal masses near Egypt’s Nile Delta, where agricultural runoff enters the Mediterranean, Gross told Ynet that no other explanation currently fits the pattern of the bloom off Israel’s coast. “In our case, I currently have no other explanation except a pollution source in the southern Gaza Strip,” Gross said.
Gross added on the social platform X that human-caused climate change has transformed the Mediterranean into an ideal breeding ground for such events, writing: “global warming had turned the Mediterranean into ‘a bathtub in August.’ Add phosphorus and nitrogen pollution and you get a deadly algal bloom. Coincidentally, in recent days there were weak, steady winds that mixed the fertiliser from the sewage along Israel’s coast. A perfect storm.” Noga Armi, chief executive of Israeli environmental nonprofit Zalul, echoed this conclusion, telling Roya News that “the scientific link is well established. Untreated sewage discharged into the sea from Gaza was one of the factors that contributed to the incident.”
However, not all researchers agree that Gaza’s untreated sewage is the main driver of the bloom. Tamar Guy-Haim, a marine ecologist at Israel’s National Institute of Oceanography, argued that the probability of Gaza sewage being the primary cause is relatively low. Researchers have so far identified the organism behind the bloom as a cyanobacterium from the genus Synechococcus, but the exact species and the full set of triggers behind its sudden explosive growth are still the subject of active investigation.
In addition to nutrient pollution, scientists have pointed to a range of other possible contributing factors: unusually warm Mediterranean seawater, strong seasonal sunlight, natural ocean current patterns, and a recent storm that increased water turbidity along the coast. Or Bialik, a researcher at Israel Oceanographic and Limnological Research, told Haaretz he had never encountered a bloom of this scale in his decades of Mediterranean work. “I’ve worked in the Mediterranean Sea for a long time and have never seen anything like this. The water is green like a lake. The turbidity is such that you can’t see your instruments after half a metre,” Bialik said.
Multiple research teams have noted the bloom appears to have originated near the Nile Delta before drifting northward along the coast with prevailing ocean currents. Looking forward, many researchers warn that even as this event is unprecedented, it is unlikely to be a one-off occurrence as climate change continues to warm Mediterranean waters. “It’s a fair estimation that this will not be a once-in-a-lifetime kind of event … you can assume that this will occur more and more through climate change,” Edo Bar-Zeev, a water researcher at Ben-Gurion University, told CNN. To date, no definitive single cause has been confirmed, with most scientists acknowledging the bloom may have resulted from a combination of warming temperatures, natural ocean dynamics, Nile Delta agricultural runoff, and Gaza wastewater pollution.