The Moving Marshes

The Moving Marshes is unrecognisable today as the area it was before The Collision. A once vibrant and colourful city on a river in the West of England. The Humans once called it Bristol.
During The Collison, much of the city and surrounding towns and farmland flooded violently, devastating buildings and infrastructure. Eventually, it settled somewhat into a half-buried wasteland.
Streets and low buildings are buried in metres of mud and brackish pools of water in some areas while others appear passable, until suddenly the tarmac shifts and bobbles underfoot, breaking apart beneath the weight of larger creatures.
The areas that used to surround the river have become vast wetlands, impassable by foot and treacherous by boat, due to hidden debris and hungry beasts that remain invisible until an unsuspecting forager finds themselves launched upon and dragged mercilessly beneath the surface, never to draw another breath.
The Moving Marshes, however, as the name implies, have been deeply touched by magic. On the Other Plane, the area was a huge and sentient swamp, resplendent in greens and blues, with vibrant bursts of colour, waiting patiently to confuse, poison, trap and drown anyone it could catch unaware. Whilst parts of the swamp remain intact Post-Collision, other areas have warped, and great towers of trees appear and disappear as they move around the wetland. These have become known as the Wandering Swamps. Geysers of mud and water 100 metres high and 50 metres across explode as if from nowhere, with little warning, and wild magic seeps from the decaying vegetation, addling minds, and causing vivid hallucinations and paranoia.
Much of the wildlife in this area is from the Other Plane, since the terra-firma inhabitants were mostly buried or drowned, and they bring changes of their own. Scorpion crabs the length of a human thigh and armoured with a spiny shell and poison-filled stinger build nests in consortiums more than 50 strong that roam slowly, constantly searching for enough food. These mud pits are much like sinking sand, invisible from a distance and almost impossible to escape once a creature falls in, even after the consortium has moved on.

Geography

The Avon River still runs through the region, although is now dominated by the wetlands. The Bristol Channel still experiences extreme tidal activity, which in turn raises and lowers the water levels across the wetlands. Much of the water is salty or brackish, although the furthest inland areas are low enough in salt that they are drinkable in some areas. Some of the more magically charged parts of the area are also free from salt water, as they are habitats for magically charged creatures who are able to keep them that way. The Buildings have mostly toppled and are slowly being eroded by the tides and vegetation that has grown rapidly, as well as the Wandering Swamps that roam the whole area.

Ecosystem

Marine and tidal creatures from the Human side of The Divide fared much better here than the terrestrial creatures. They have not escaped the volatile magic and warfare though, and mutations can be seen in many species.
Many sentient or semi-sentient flora and fauna call the Moving Marshes home. From the aforementioned Scorpion Crabs to giant salt-water crocodile type creatures with six legs and snake-like fangs, to seals and marine fish of all sorts.  Frogs and toads in sizes ranging from palm-sized to car sized have claimed territory in buildings and trains. Birds who stalk the waters for fish and weeds, and nest in the Wandering Swamp claim the skies here.  Long legged deer and light-footed stoats occupy the inland areas, finding food and shelter where they can.  It is a vibrant, alive place, full of unseen dangers.

Ecosystem Cycles

The Moving Marshes are at the mercy of the seasons, which still follow the lunar and solar cycle of the planet. The Wandering Swamp carries it's own micro-climate, the humidity and warmth generated by the magic within the flora, providing exactly what it and it's fauna inhabitants need - like a roving terraium, without the glass bubble.

Localized Phenomena

The Geysers are a phenomenon that has occurred as a result of The Collide, neither side of the Divide had experienced anything like it before.  The enormous jets of water and mud explode at random from the marshes, propelled by natural gases and magic.  They vary in size from a few centimetres to a hundred metres high and tens of metres across, and can last from a few seconds to around a minute. 
The Wandering Swamps can only be found here, speculations suggest that there are only two or three, but as they move entirely at random, they are impossible to follow and record with any reliability.

Climate

The climate is similar to that of Pre-Collision Britain.  Effects of anthropogenic global warming have been greatly reduced since the destruction of almost all sources of fossil fuel activity were destroyed.  However, weather systems have been influenced by The Collision and electrical storms are much more common across the entire planet, including the Moving Marshes.

Type

Wetland / Swamp