It's a Charles Kingsley (1819–75) Poem

Notes:

"the harbor bar be moaning"--This refers to an old legend from the fishing towns of western England. The "bar" is a sand bar across the entrance to a small harbor. It is this bar that keeps the water comparatively still and calm inside the harbor. More affluent towns would build up a stone wall on the bar, making a mole. In its unimproved state, however, the bar was visible above the water, if at all, only at low tide. In the days of sail, ships and fishing boats would leave the harbor as the tide withdrew. The legend was, that if the withdrawing tide made a moaning sound over the bar, that was a portent of disaster. (In some versions, the moaning of the bar was a tribute to a death that had already occurred.) The moaning of the bar is most famously used in Tennyson's poem "Crossing the Bar."   

From: http://olimu.com/Readings/ThreeFishers.htm