At first the captain stood dumb with amazement, and he was just about to call out, when Ralph shouted again.
"I swam over," he said, "but I can't get back.

I've got the cramps.
Can't you make some sort of a raft, and come over to me! The water's awfully cold." Raft, indeed! There was no material or time for anything of the kind.

If the boy dropped off that bit of rock, he would be drowned, and the captain did not hesitate a moment.

Throwing aside his jacket and slipping off his shoes, he let himself down into the water and struck out in Ralph's direction.

The water was, indeed, very cold, but the captain was a strong swimmer, and it would not take him very long to cross the lake at this point, where its width was not much more than a hundred feet.