(CNN) -

U.S. airstrikes helped Kurdish and Iraqi forces take control of Mosul Dam on Monday, fighting back ISIS militants who had seized the dam, President Obama told reporters.

The stakes were huge for the millions of Iraqis who live downstream from the dam, the largest in the country.

"If that dam was breached it could have proven catastrophic, with floods that would have threatened the lives of thousands of civilians and endangered our embassy compound in Baghdad," the President said.

The dam has been the center of an intense battle in northern Iraq between the Islamic extremists and Kurdish forces that had been fighting to retake it since Saturday with U.S. air support.

"The U.S. military used fighters, bombers, attack and unmanned aircraft to conduct 35 strikes, " said Pentagon spokesman Rear Adm. John Kirby. "We destroyed over 90 targets including a range of vehicles, equipment and fighting positions," he said.

Now that the dam is cleared of ISIS militants, Iraqi forces are moving to grow their area of control, the Pentagon said.

"This operation demonstrates that Iraqi and Kurdish forces are capable of working together and taking the fight to ISIS," Obama said. "If they continue to do so, they will have the strong support of the United States of America."

Taking the fight to ISIS

U.S. airstrikes may not be enough to do the job of ridding Iraq of ISIS forces, said retired Col. Cedric Leighton, a former Air Force intelligence officer.

"At the core of the mission is to get rid of ISIS," he said. "The U.S. cannot have a Middle East in which ISIS exists," he said.

The brutal attacks of ISIS militants as they took control of towns and villages in northern Iraq forced hundreds of thousands of people to flee.

"ISIS tells people to pay or convert," said one Christian man who fled ISIS forces.

A Christian village near Mosul Dam is almost deserted. Some of its residents fled just in time to a monastery in the mountains.

"We were afraid, terrified they'd call us infidels," a Christian woman there told CNN's Nick Paton Walsh. "My Muslim friend told me to just leave."

Now she said she hopes ISIS fighters won't reach the monastery.

The U.S. strategy in fighting ISIS is "to take out Isis' leadership, to degrade their operational capabilities, to cut off their financing sources," U.S State Department spokeswoman Marie Harf said Monday.

On several ISIS websites, the group posted a message Monday threatening that "America will disappear from the map soon on the hands of knights of al-Khilafa," a reference to the caliphate ISIS claims it wants to recapture.

Water in war

When ISIS militants seized the dam this month, many feared it could be used as a weapon.

Built in the early 1980s under former Iraqi dictator Saddam Hussein, the dam sits on the Tigris River about 50 kilometers (30 miles) north of the city of Mosul. It serves as a key source of electricity, irrigation and flood protection.

ISIS has a track record of attacking its enemies with water.

This year, its fighters opened the gates on the Falluja Dam in central Iraq after seizing it in an effort to stop an Iraqi military advance. The water from the dam flooded a number of villages.

"ISIS has already used other smaller dams to gain control of territory, to pressure Sunnis to support them and to punish the Shiites," Daniel Pipes, president of the Middle East Forum, told CNN this month.

The 3.2-kilometer-long Mosul Dam holds back as much as 12.5 million cubic meters of water, according to Engineering News-Record, a construction industry website.

If the structure were to give way, it would unleash a wall of water tens of feet tall that would race down the Tigris toward Mosul and its 1.7 million inhabitants. It would also bring flooding to major cities farther downstream, including Baghdad.