Blast! just remembered Martyn Wyndham-Read BALLAD OF THE DROVER

The faithful dog a moment
    Sits panting on the bank,
And then swims through the current
    To where his master sank.
And round and round in circles
    He fights with failing strength,
Till, borne down by the waters,
    The old dog sinks at length.

I cry like a baby everytime I hear it.