What will be the impact of flooding Gaza’s tunnels with seawater?

Before Israel’s relentless bombardment of Gaza, access to clean water in the besieged enclave was already scarce for Palestinians. It could be about to get even worse.

Israel’s military has begun pumping seawater into tunnels used by Hamas in Gaza, according to a report in the Wall Street Journal on Wednesday.

The WSJ, citing US officials, reported last week that Israel had finished assembling at least five large seawater pumps near al-Shati refugee camp in northern Gaza. The pumps can draw water from the Mediterranean Sea and move thousands of cubic metres per hour.

Israeli officials are reportedly contemplating a plan to flood the tunnels over several weeks, in an attempt to dismantle the network and weaken Palestinian armed groups.

Researchers specialising in water, diplomacy and conflict have told Middle East Eye that the flooding would have damaging ecological effects, including the pollution of Gaza’s already devastated water supply and damage to its crops

The impacts could amount to a breach of international humanitarian law, according to one of the experts.

Israel has not officially given any details about the flooding plan, deeming the information classified. The length and intensity of the proposed measure is therefore unknown.

“While the overall scope and magnitude of the impact is unclear, we can reasonably expect that at least some seawater will be seeping into the soil from the tunnels, particularly in areas where tunnels have previously been damaged,” Juliane Schillinger, a researcher at the University of Twente in the Netherlands.

Schillinger, who specialises in the interaction between conflict and water management, said the seepage would lead to localised pollution of soil and groundwater with seawater.

“It is important to keep in mind that we are not just talking about water with a high salt content here – seawater along the Mediterranean coast is also polluted with untreated wastewater, which is continuously discharged into the Mediterranean from Gaza’s dysfunctional sewage system,” she said.

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Damage to agriculture

Gaza’s coastal aquifer, the only water source in the besieged enclave, is already polluted due to over-pumping and sewage.

The water is intermittently supplied to Palestinians in the territory via pumps controlled by Israel. At the start of the current conflict in early October, Israel turned the pumps off completely for several days.

Around 96 percent of household water in Gaza is contaminated and not fit for human consumption. As a result, most Palestinians in the strip rely on unregulated private water tankers and unlicensed desalination plants.

Water from these plants is often still contaminated, according to a 2021 study. Israel’s war on Gaza has forced at least three major desalination plants to cease operations.

“The very poor quality of the water in Gaza is the result of a situation in which there is no meaningful space for the Palestinians to determine their own water governance,” Michael Mason, professor of environmental geography at the London School of Economics.

Mason blamed that lack of governance on “the sustained and disabling effects of the Israeli blockade, economic de-development and recurrent armed conflict”.

He added that any prospect of post-war reconstruction of water infrastructure would rely on access to the aquifer, which would be further salinated and polluted by the flooding plans.

“Already the war has degraded further the aquifer, as a consequence of damage to wastewater infrastructure and the leakage of heavy metals from the indiscriminate use of munitions,” Mason said.

Schillinger noted that in the event of Hamas storing toxic materials in the tunnels, pollution could be exacerbated by the washing out of such substances into the soil and groundwater.

The seawater flooding would cause long-term damage to Gaza’s agriculture too, which has long been ravaged by Israeli action.

“Agricultural use of the land has been severely impacted by military attacks, occupation and the displacement of the population,” Mason said.

“Assuming that the agricultural sector can somehow be resurrected in the future, the salt-laden groundwater will greatly constrain crop choices.”

In addition to the environmental impact, the flooding plan has also raised concerns about the safety of Israeli captives, taken during Hamas’s attacks on southern Israel on 7 October, who may be being held in tunnels.

Last month, some of the captives released by Hamas shared testimonies of being held either in underground tunnels or in hideouts.

International law breach

It wouldn’t be the first time the tunnels have been filled in an effort to weaken Hamas – Egypt flooded the networks with sewage in 2013 and with seawater two years later.

Cairo did so in efforts to prevent the alleged smuggling of weapons, resources and fighters between southern Gaza and the Sinai peninsula.

The seawater flooding eight years ago led to civilian homes and businesses being waterlogged in Gaza, as well as damage to water supplies and farmlands.

Israel will likely argue that the flooding of tunnels is “proportionate” as a military objective under international law, due to the networks’ use by Palestinian fighters.

Mason noted, however, that actions which cause long-term damage to the environment are unlawful.

“Sustained and extensive flooding of the tunnel network would breach those norms of customary international humanitarian law that prohibit means of warfare intended, or that may be expected, to cause widespread, long-term and severe damage to the natural environment,” he said.

“Such a breach of international humanitarian law is made more probable given that the aquifer is essential to the water needs of the civilian population and is already on the tipping point of long-term collapse.”

Middle East Eye reached out to the Israeli military on the impact of flooding the tunnels, but did not receive a response by the time of publication.