Seamus Heaney's poem, "Casualty," is about a man who is killed during the civil war between Ireland and Britain, being in the wrong place at the wrong time, after being told (with the other "men in Derry") to observe the curfew.
The speaker describes the man, and though the man is an old tar and the narrator is a "poet," they get along well enough, and the narrator greatly admires him.
There are a number of references to water or things associated with water: the man in the pub wears "waders and a peaked cap;" there is mention of his "fisherman's quick eye;" and, the speaker moves their conversation to "eels."
Part II also mentions water, but here it is used to describe the day of the funeral when those killed in the Bloody Sunday massacre in the 1970s are buried:
Coffin after coffin
Seemed to float from the door
Of the packed cathedral
Like blossoms on slow water.
The focus of the poem then shifts back to the fisherman. The reader learns that he was killed going out for a drink after curfew...
He had gone miles away
For he drank like a fish
Swimming towards the lure
Of warm lit-up places...
In Part III, the speaker notes that he missed the fisherman's funeral, but into his mind's eye comes a memory when the two men went out on the first man's fishing boat:
On the water, the land
Banked under fog: that morning
I was taken in his boat,
The Screw purling, turning
Indolent fathoms white,
I tasted freedom with him.
The narrator continues to describe that morning—going out early to catch the fish, developing a rhythm in the work, "in your proper haunt." Subtly the narrator has begun to speak to the fisherman in his memory. And he brings the images of the two aspects of the man together at the end:
...the fisherman—now a ghost (perhaps the speaker feels this way through his memories of their day on the water, fishing); and the drinker, the law breaker—and the casualty...
Plodder through midnight rain.
The eNotes source on Heaney's poem cites its similarity to William Butler Yeats' poem, "The Fisherman." Yeats' character was similar to that of Heaney's—a man alone, anonymous. But the critic notes the references to water:
It seems, however, that the poem needs a sense of the sea...
The critic then points out use of the words "fathoms," "haul/ Steadily off the bottom," "well out, beyond," and mentions that this "sense of the sea" lifts one...
...to give a sense of scope to the freedom being "tasted."
Certainly the fisherman experienced a freedom on the water that was not allowed to him (or anyone else) because of the fighting raging all around.
There is also a furtive side to the fisherman. This imagery can be seen in several descriptions, such as "...Sure-footed but too sly; "His fisherman's quick eye;" his "observant back;" and, "he would not be held / At home by his own crowd." Here is imagery that suggests he was up to some kind of mischief—going where he shouldn't; refusing to be directed. This ties in with the speaker's question as to whether the fisherman was somehow to blame for his own death. However, his furtive movements seem more to suggest his need to be free, and not only his discomfort for being controlled, but also his refusal to be tied down.