BY Mohammed Omer

Some 2,000 men and boys work in the tunnel trade in the Gaza Strip. But over the past three months, more than 80 percent have lost the only work and benefits available in besieged Gaza, which remains stuck in an Israeli blockade.

That occurred after the government of Egyptian President Mohammed Morsi ordered the destruction of the underground transportation network. As part of that effort, the military began dumping raw sewage into the passageways.

It's the most serious - and arguably the most dangerous - attempt by Egypt to close down the tunnels since 2006, when Palestinians began digging the warrens after Israel sealed off its borders with Gaza following Hamas' election victory.

An estimated 30 percent of goods that reach Gaza's 1.7 million Palestinians come through the tunnels.

Heralded by Israel as a necessary step to prevent weapons sales into Gaza and to keep attackers out, the blockade has resulted in Palestinians being cut off from many essential items such as food, fuel and building materials.

Egypt frequently seals its border in Rafah citing security concerns, as attackers have launched assaults on security forces on the Sinai peninsula by using the underground network. 

Hundreds of tunnels have been burrowed over the 14-kilometre stretch of land linking Egypt to Gaza. 

The transportation lines have come at a cost. Israel's Air Force frequently bombs them, resulting in the deaths of at least 20 Palestinians by direct missile hits, according to statistics from the Al Mezan Center for Human Rights.

One tunnel owner who identified himself as Abu Suliman said only 50 tunnels are functioning, as opposed to about 550 working at full capacity following Israel's last military operation on Gaza in November 2012.

Egypt's Interior Ministry spokesman, Islam Shawan, estimates about 900 tunnels had been operational between Gaza and Egypt until the recent campaign to flood them with sewage water.