Hard ground eluded his feet as he sloshed through the ambiguous and shifting layers of mud, water and slimy plants. He followed as best he could the erratic pathway as he leapt from one patch of ground to the next, squelching and sliding through the indeterminate muck between the firmer points. Ahead the terrain stretched out like a fine green carpet interspersed with pools of darkly reflecting water, behind he had left a track of muddy foot prints, holes that rapidly filled, and in the truly wet places, roiling clouds of black mud. All around them towered the trunks of immense trees, their roots rising like ancient fortifications from the creeping mud, hung here and there with the ragged banners of vines and creepers, and sometimes a threadbare brocade of vivid flowers.
The swamp thickened and deepened into a murky gloom, the air lying heavy and still and redolent with rotting leaves, stale water and the sweet heady scent of flowers. He slumped down onto a half rotted stump and watched as a deep blue beetle made a slow progress across a fallen twig, like a jewel being pushed down a rough thread. He leant forward on his perch, to better see the glinting bug, when suddenly the remainder of the stump he was sitting on gave way, and he tilted forward alarmingly, flailing for some purchase to stop himself from toppling face down in the black water. He finally managed to grab at his treacherous seat, and plunged his hand down into the soft mass of flaking, powdery wood, only to fall forward anyway as whatever he grabbed came away. He hit the water with a cry and a splash, and slid into the dankest, foulest muck of rotten plants and stringy chunks he feared to identify. Oily and thick, the swamp coated his skin like a feculent suit of armor. Sweeping frantically at the slugs of slime sliding down his face and neck, he threw up again. The smell....
Struggling to his feet, he stood in knee-deep foulness of filth. He could see the path here and there like humps of a great sea serpent breaking the surface of the swamp. Taking a step toward the nearest island, the slime slurped loudly as his foot struggled free. Ten paces to the relatively clear land seemed like miles.
Panting, he rested his aching thighs and swiped the sweat from his forehead. Gnats swirled around his head, his face already swollen from their bites. Damned bloodthirsty little suckers.
I hope I don't see any snakes. I hate snakes. If the gnats are so big, how big could the snakes get here? I won't think about it. One foot in front of the other, that's all I need to think about right now.
Listening to that internal voice of reason, he started for the next safe ground. Wearily, he hauled his foot free of the slime, took a step, and no swamp bottom met his foot. Falling off the edge of a hidden canal, he fought again to keep my head above the foul gelatinous muck. He might as well have tried to swim through tar. His boots began to drag him under, and there was absolutely nothing he could do. And then, something writing wrapped itself around his torso...
Too tired to even cry, he surrendered.
From various sources, including this page and this page (a journey through sludge) and a little of my own tweaking.