Symbolism, Imagery, Allegory
If you were a little grossed out by all the swamp talk and creatures, don't worry—we were too. But the swamp and its many creatures are pretty important in this book. It's not just about slime and ooze and deadly creatures in the dark; no, these things represent something more.
The swamp and its inhabitants represent the world before modern technology took over. Though we might not be able to appreciate the mud and gunk of it all, the magic of it all is still pretty, well, magical. This magic—this mysterious and beautiful nature—is threatened by mankind's desire to improve things, which begs the question: Is it really improvement to kill off an entire way of life?
In the swamp there is mud and gunk and smelly things, to be sure, and there are also Horrors that scream and scare and even kill folks. In other words, there's some seriously Dark Magic in the mix. We wouldn't be doing the swamp justice, however, if we didn't also mention the swans who live there, Mucky Face who tries to save Briony, or the cute Bleeding Hearts that beg for a love story. Even sulky Briony can't deny the pleasantness of them when she says:
I'd forgotten how prettily their voices chimed together. (19.43)
If it wasn't for the swamp, none of these magical elements would exist—and in this way, the swamp represents the magic of our natural world or environment. But look at what's happening to the swamp:
[…] Mr. Clayborne's official business, which was to drain the water from the swamp. This was going to improve life in the Swampsea, at least according to Queen Anne. Less water meant more land. More land meant more crops, and more grazing for sheep and cattle. More land also meant no swamp. (3.46)
Always looking to improve things, the men of Swampsea are threatening natural magic in hopes of improving life for the citizens of Swampsea. While all of the benefits Briony notes may be true, it also means that the lives of many creatures and spirits who reside in the swamp will cease. When Briony reflects on Eldric's interest in the swamp, she notes that:
London seems an exciting place, far more exciting than the Swampsea. But it occurred to me that the Swampsea might seem equally exciting to Eldric. He wouldn't have seen any of the Old Ones: So many had died in the great cities. (6.76)
Here we see the downfall of modernization, as it is killing off Old Ones and the natural life that exists in the swamp. The question remains: Do the benefits justify the cost? You be the judge.