The literal meanings of the lines themselves and the overall meaning of the poem are very similar in this poem by Oliver Wendell Holmes because it is written as a dialogue with a story.
There was a tall, young oysterman who lived by the river. He ran a shop on the bank, and his boat was just underneath it. A pretty woman lived on the opposite side of the river from him with her father, a fisherman. The oysterman was thinking about his love one day while watching her from afar. He saw her waving her handkerchief, as much as if to say, "I'm wide awake, young oysterman, and all the folks away." In a rush, the oysterman jumped up and thought I guess I'll leave the skiff at home, for fear that her parents should see; I read it in a story-book, that, for to kiss his dear, Leander swam to Hellespont, so I could swim this, here. And so, he swam across the river to reach his fair lady and to receive her beautiful kisses. But, suddenly, they heard the footsteps of the lady's father, so the oysterman quickly jumped back into the river to swim home. The old fisherman asked his daughter what the splashes were about, and the daughter replied, "'T was nothing but a pebble, sir, I threw into the water." Then, the father asked what it was paddling off so fast, and the daughter again protects the oysterman, saying it was a dolphin. The old fisherman tells her to fetch his harpoon, then, so they will eat it for dinner that night. The daughter had nothing to do but turn pale white. While trying to swim back home, the oysterman falls victim to a cramp and drowns in the current. Now, the oyster shop is commemorating the fallen boy and selling oysters to "mermaids down below."
I suppose I could be redundant by saying that there is a lot of imagery, but that would be silly because the whole thing is a story about something that happened. It was written to be played in your head.
This hidden love does not endure because God gave lungs to humans, not gills. The poor boy only wanted to hold his dream in his arms, but he was not certain how her father would cope with it, so he tried to hide his love for her. When he thought he had the chance, it was tarnished, and he paid the ultimate price for his poor timing.