Mader's team, Bahrain Victorious, announced the sad news Friday morning ... explaining the Swiss rider was initially hurt after he lost control of his bike while traveling at a high rate of speed on a downhill portion of the race's Stage 5.

Tour de Suisse organizers said Mader tumbled into a ravine as a result of the wreck ... and when medical personnel first found him, he was laying motionless in a body of water.

Mader was able to be resuscitated at the scene and then airlifted to a nearby hospital ... but he passed away hours later.

"Despite the best efforts of the phenomenal staff at Chur hospital, Gino couldn’t make it through this, his final and biggest challenge," Mader's team said, "and at 11:30 a.m. we said goodbye to one of the shining lights of our team."

Bahrain Victorious officials added, "Gino was an extraordinary athlete, an example of determination, a valued member of our team and the whole cycling community. His talent, dedication, and passion for the sport has inspired us all."

Despite the tragedy, the Tour de Suisse will continue ... and before Friday's Stage 6 kicked off, other cyclists gathered in a circle to pay their respects to Mader.

"Gino," Mader's team said Friday, "thank you for the light, the joy, and the laughs you brought us all, we will miss you as a rider and as a person."

Mader was just 26 years old.