Her mind is as secret from her
As the water on which she swims,
As secret as profound as ominous.
Weeping bitterly for her ominous mind, her plight,
Up the river of white moonlight she swims
Until a treacherous undercurrent
Seizing her in an icy amorous embrace
Dives with her, swiftly severing
The waters which close above her head.
An enemy sentinel
Finding the abandoned clothes
Waits for the swimmer's return
('Come on, come back')
Waiting, whiling away the hour
Whittling a shepherd's pipe from the hollow reeds.
In the chill light of dawn
This line is the title of the poem and the title of a war song, referring to the longing of soldiers' families for them to return. But in this context it encapsulates the poem’s ambiguity, and is itself multi-layered. ‘Come on’ implies that the sentinel is urging her to continue to swim until she is drowned; ‘come back’ is a command to return to the lakeside and either be saved or be arrested. It may be that, out of humanity, he wishes her to be spared. It is left unexplained for the reader to interpret. 
 The sentinel presumably doesn’t know that she is already drowned, probably now at peace and maybe more fortunate than those who have to face life in a war-damaged world.
Come On Come Back