EIN GEDI (AP, AFP) — A multinational group of swimmers swam seven hours through the salty, soupy waters of the Dead Sea on Tuesday in a bid to draw attention to the environmental degradation of the fabled lake.

At dawn, the 25 swimmers left on boats from Ein Gedi on the Israeli side of the Dead Sea to Wadi Mujib on the Jordanian side. Then, wearing special protective masks and snorkels, the swimmers paddled through the thick waters in what turned into a 17-kilometer (11-mile) swim from Jordan to Israel.

Swimming in the Dead Sea is unusual. Tourists typically dip themselves from the beaches and float on the water with the help of the lake’s high salt concentration. It also draws people from around the world who believe the water’s high mineral content is beneficial for skin conditions.

The Dead Sea, the lowest place on earth at 423 meters (1,388 feet) below sea level, has shrunk significantly over recent decades, a process environmentalists blame on unsustainable water management and over-exploitation of the lake’s minerals.

“We’re here for the first ever Dead Sea swim challenge with 25 swimmers that come from all over the world to send out a clear message to save the Dead Sea, which is shrinking today at an alarming rate,” said Mira Edelstein, from the environmental group EcoPeace, one of the swim’s organizers.

People swim in the salty waters of the Dead Sea, from Jordan to Israel, arriving at Ein Gedi, Israel, Tuesday, Nov. 15, 2016. Swimmers from around the world plunged into the salty waters of the Dead Sea in a bid to draw attention to its environmental degradation. Wearing protective masks and snorkels, 25 swimmers paddled through the muddy water to attempt the 10-mile (17-kilometer) swim from Jordan to Israel. (AP Photo/Ariel Schalit)

People swim in the salty waters of the Dead Sea, from Jordan to Israel, arriving at Ein Gedi, Israel, Tuesday, Nov. 15, 2016. Swimmers from around the world plunged into the salty waters of the Dead Sea in a bid to draw attention to its environmental degradation. Wearing protective masks and snorkels, 25 swimmers paddled through the muddy water to attempt the 10-mile (17-kilometer) swim from Jordan to Israel. (AP Photo/Ariel Schalit)

Organizers say the Dead Sea’s water level has fallen more than 25 meters (80 feet) over the last three decades. The lake’s southern basin, disconnected from the shrinking northern side, has seen flooding in recent years because of heavy industrialization.

The swimmers, who hailed from Israel, the Palestinian territories and as far as New Zealand, South Africa and Denmark, wore special face masks to shield them from the briny water, which is painful to the eyes and can be deadly to ingest. The group, the oldest of whom was 68, was accompanied by support vessels with medical equipment and food.

Despite the tough conditions, only three swimmers failed to finish — two who suffered from dehydration and a third who complained of chills.

Four swimmers took breaks on the medical vessel. Palestinian lifeguard Yussuf Matari, 61, was treated with an IV as he rested in the shade of a boat’s tarp before plunging in to the waters again.

Gidon Bromberg, EcoPeace Middle East co-director, said the event was “a global call to save this amazing sea.”

“This is the lowest place on earth, these are the deepest saline waters on the globe, a unique composition, and sadly for the last 50 years they have been dramatically on the decline,” he said.

Group of swimmers who attempted a seven-hour swim across the Dead Sea in from Jordan to Israel a bid to draw attention to its environmental degradation pose for a photograph on November 15, 2016. (EcoPeace Middle East)

Group of swimmers who attempted a seven-hour swim across the Dead Sea in from Jordan to Israel a bid to draw attention to its environmental degradation, November 15, 2016. (EcoPeace Middle East)

Jackie Cobell, a British long-distance swimmer, called the Dead Sea swim “historic and iconic,” before descending into the water. “This is really important because it’s disappearing fast.”

Those who neared the shoreline first waited so all could finish the race together. Speakers blared “We are the Champions,” the iconic hit by the English rock band Queen.

“I must say that I did not expect this swim to be so hard and what was really, really tough conditions is that salt. Constantly trying to get the salt out of your mask and the chafing,” said Jean Craven, a founder of “Madswimmer,” a South African charity that participates in open water swims around the world to raise money for children’s causes.

“This was a challenge, not a race,” he added. “It was really great to see the camaraderie, you know, everyone trying to bring the slowest swimmers along with them.”

The mineral-rich lake was calm, but the high amount of salt in the water makes it nearly impossible to swim normally.

It has 10 times more salinity than the Mediterranean Sea, meaning bodies float to the top, and keeping under the water is difficult.

“It was tougher than we expected,” said Samuel Moran, a 40-year-old Spaniard.

“The worst was the sun and the feeling of the salt on your skin that is very irritating. You feel like you are burning all the time,” he said, adding he felt like quitting “many times”.

Kim Chambers from New Zealand said she had swam extreme routes across the globe but this presented a unique test.

“Even just a few drops (of water) feels like acid burning in your eyes — if you ingest it, either through your mouth or through your nose, it is potentially fatal.”

A woman taking part in a 18-kilometre swim from Jordan to Israel across the Dead Sea, organised by the EcoPeace charity aimed at raising awareness for the iconic water body which has been receding by roughly a metre each year, gives the thumbs up upon the departure from Jordan on November 15, 2016. (AFP PHOTO / Gali TIBBON)

A woman taking part in a 18-kilometre swim from Jordan to Israel across the Dead Sea, organized by the EcoPeace charity aimed at raising awareness for the iconic water body which has been receding by roughly a metre each year, gives the thumbs up upon the departure from Jordan on November 15, 2016. (AFP PHOTO / Gali TIBBON)

The Dead Sea’s degradation started in the 1960s when Israel, Jordan and Syria began to divert water from the Jordan River, its main source, largely for irrigation.

The water level has dropped around 40 metres since its peak, said Yechieli Yoseph, a hydrogeologist with the Geological Survey of Israel.

Companies also take out water to use the minerals inside it for medical purposes, Yoseph added.

More than 4,000 sinkholes have also formed along the Israeli, Palestinian and Jordanian coasts since the 1980s, according to Israeli research, with more than 400 per year in recent years.

“The Dead Sea is going down mostly because we have changed its water balance — we meaning Israel, Jordan and Syria,” said Yoseph.

“Of the water that used to come to the Dead Sea, 90 percent of it or more is now being taken.”