The mens' bodies were pulled from the water last night.
Friends and family of the 19-year-old victim were reportedly there as rescuers recovered his body.
Henderson said the man who tried to save his friends was "hysterical". He told Nine News: "He was just rolling on the floor, crying, and just devastated".
Senior Sergeant Mark Smith said the men were affected by alcohol.
"Unfortunately because of the effects of alcohol, two of them have got into trouble while swimming across the lake," he said at the scene.
The lake's visibility is poor and the water is extremely deep, with a layer of floating mould and debris, according to Henderson.
Residents in the Mill Park community have expressed their grief on social media.
"This is so terribly sad for their families and the community. The innocence of the lake is now tainted by the memory of these poor mens' deaths," one woman wrote.
- AAP