Fahmi al-Abrak, 70, was at home on March 27 when a lagoon of human waste broke through its sand embankment and hurtled downhill, inundating this poor village of Bedouins in northern Gaza. “It rose to here in 15 seconds,” he said, pointing to a discolored line on the walls, four feet above ground.

Five people were drowned when the overflow pool for a lake of water and human waste failed in March.

Residents of Umm al Nasser pulled belongings from their homes after the wave of sewage struck their village in March.

Five people died, drowned in the wave of waste, along with scores of goats, sheep and chickens. Nearly 1,000 people had to be taken out of the village. Now, Mr. Abrak said, “I’m afraid to go to sleep at night.”

The lagoon disaster seemed a sort of metaphor for Gaza — overcrowded, lacking in resources, coping with makeshift answers to long-term problems. But the lagoon, which held more than 150,000 cubic yards, is dwarfed by the huge lake of sewage it was built to reduce.

That lake, which itself holds sewage overflow, now contains almost four million cubic yards of water and human waste, covering about 100 acres, and it is again creeping close to the danger point. Its sand embankment was reinforced this summer, and two more outlet ponds have been dug in the sand. But more waste enters daily than is discharged, the lake is only six feet below the embankment and the winter rains are coming.

And yet a project to fix the problem is stalled by politics and conflict. Israel has declared Gaza “hostile territory” and is sharply limiting the kinds of goods allowed in.

The restrictions cover many ordinary items not considered essential to human life. But they also cover things like metal pipes, welding machines and the wire used to refurbish electric motors — things that Israel believes could have secondary use by the Hamas administration and the Palestinian gunmen who fire rockets toward nearby Israeli towns like Sderot.

Israel, obliged to protect its citizens, is trying to press Hamas both militarily and economically. It says it will now reduce supplies of diesel fuel, gasoline and even electrical power in response to recent rocket barrages.

But as Mike Bailey of the aid group Oxfam pointed out, the pumps that drive sewage treatment run on electricity and fuel, as do those that pull drinking water from the very aquifer the sewage treatment system was originally designed to replenish.

He said the level of the lake was one problem, and the rain’s effect on the sand embankment was another. “There could be a break, or if there’s an overflow, it will carry the embankment with it, like New Orleans,” he said. “Large quantities of water and sewage will travel downhill fast.”

But the pumps have been moved to the teeming city of Khan Yunis, where another sewage disaster is threatening. Trying to save money, residents there hooked their sewer pipes to a system to catch rainwater and have filled it with waste, creating a sludge that blocks drainage. With the coming rains, that system threatens to overflow, forcing sewage back into homes and businesses and polluting the aquifer and the wells that supply most drinking water.

A Japanese project for repairs at Khan Yunis was suspended when Hamas won Palestinian elections in 2006. So the International Committee for the Red Cross is helping to build two pits for the overflow, but pumps are needed to get the sewage up to the pits, which are not yet built.

Even before this latest crisis, a World Bank project to replace the northern facility and drain the lake into nine new treatment ponds was delayed for nearly two years. The area had suffered from warfare with Israel, internal Palestinian clashes, strikes by workers and other problems.

But Israel has also restricted the import of steel pipe from two to six inches in diameter, wire mesh, cement, welding machines and pumps, saying Hamas can use all of them to build bunkers, as Hezbollah did in southern Lebanon, or to make rockets.

Anthony Dalziel of the Red Cross said his organization had no trouble importing medicine and did not criticize Israel’s security concerns. But the results, for the sewage crisis, have meant “a lot of temporary solutions that are supposed to be for six months and end up having to last six years,” he said.

“It’s indicative of the infrastructure crisis here,” Mr. Dalziel said. “Everything is linked to access into Gaza of materials, cement, fuel, parts, electrical transformers and engineers. So we struggle to create ad hoc solutions as opposed to better, cheaper, permanent ones.”

Monther I. Shoblak, director of the Gaza Emergency Water Project for the Palestinian Authority’s water utility, said he needs the materials, not more money, adding: “Almost nothing of what I need has been allowed to enter Gaza since May.”

If the lake overflowed, he said, “it would be a tsunami of waste.” In three seconds, he estimated, more than 800 homes and 10,000 people would be hit by a wave up to six yards high, and then the wave would return. Oxfam estimates that 50,000 people could be displaced and 200,000 affected.

Shlomo Dror, spokesman for the Israeli authority that coordinates with Gaza, said Israel was coordinating with the World Bank and would prefer the use of plastic pipes, which Israel uses, and not steel, which project engineers insist is necessary near the pumps to deal with the pressure.

The lagoon broke in March, he said, “because there is no security there and people were stealing the sand.”

His boss, Col. Nir Press, said Israel has met regularly with the World Bank and other agencies, has allowed the import of parts and pumps and may allow some steel pipe, if there is a credible guarantee that it will not be used in making rockets. “We don’t want this disaster, either,” he said. “I don’t think they’re working urgently enough. I assure you we are as concerned as they.”

Mr. Shoblak, the water utility official, is working on another patch: a third treatment pond, for which he needs Israeli permission, and two more mobile pumps to replace those now in Khan Yunis. Most of all, he said, “I need pipes.”

Mr. Bailey of Oxfam said that Mr. Shoblak was “a juggler doing well with old equipment.” But since June, few spare parts have been imported to repair his old pumps, which serve 33 sewage pumping stations, 130 drinking water wells, three treatment plants and four storm water pumping stations. “It’s like flying a plane with all the needles in the red,” Mr. Bailey said. “Without spare parts, you can fall out of the sky.”

Mr. Shoblak put it differently. “How many Palestinians need to drown?” he asked.