PARIS (AP) — Engineers in France have started work to drain an immense lake that has built up under an Alpine glacier on Mont Blanc, an attempt to prevent a repeat of a flood that killed 175 people more than 100 years ago.

Specialists are drilling into the glacier as part of preparations to slowly pump out the 65,000 cubic meters (2,275,000 cubic feet) of liquid believed trapped beneath the Tete Rousse glacier, the mayor of the Alpine town of Saint-Gervais-les-Bains said Wednesday. The amount of water is equivalent to about 26 Olympic-sized swimming pools.

So far, the delicate, nearly euro2 million ($2.5 million) operation in the area well-known for its climbing and skiing is going smoothly, and pumping is expected to start imminently and last until October, Mayor Jean-Marc Peillex told The Associated Press.

"The town didn't want to wait for a catastrophe — we are taking action to prevent one," said Peillex, whose spa town of 3,000 people would likely be in the flood path were the water to burst out.

The glacier is situated 3,200 meters (10,560 feet) up Mont Blanc, and is on the most popular paths for climbers scaling Western Europe's highest peak.

Scientists studying the glacier informed local authorities about the trapped water in March. Since then, officials have shut down part of a tram route used by Mont Blanc climbers and installed an alarm system in case of flooding. If it goes off, residents have between 10 to 30 minutes to evacuate.

Despite the precautions, officials and scientists say the glacier is unpredictable. In a letter posted on the town's Web site, the mayor wrote: "Nobody can say the risk is imminent, and nobody can say there's no risk, either."

Water from the glacier has devastated the valley before. In 1892, flood waters burst from the buried lake, killing 175 people. The amount of water currently believed trapped is comparable to what caused the 19th century flood, the mayor's office said.

When pumping starts, it will relieve pressure inside the glacier, the mayor said.

"Once they take out the first few dozen cubic meters (of liquid), that doesn't mean there will be zero risk, but there won't be at all the same level of stress that there is today," Peillex said.

Switzerland-based glacier expert Martin Funk, who is not working on the project, called the Tete Rousse glacier "a special case."

"There are very special conditions in that the water is trapped in the glacier and doesn't flow out as it usually does," said Funk, of the Swiss Federal Institute of Technology in Zurich. He added: "This is certainly not a direct consequence of global warming."

Funk said there were unanswered questions about the glacier, such as what the conditions were like in the glacier between 1892 and now.

"It's possible that all this time some water was trapped inside the glacier and nothing happened — we don't know that," he said.