Wetlands are defined as areas that have (more or less) standing water at or above the surface most or all of the time. Thus, they include marshes, ditches, wet grassland, reed beds, carr woodland (wet woodland, typically of alder and/or willow), lakes and ponds. In many instances, more than one habitat type is present in the same place, e.g. a pond can have margins of marshy grassland and perhaps some reeds and even a patch of wet woodland nearby. Each of these habitats has its own characteristic suite of associated flora, living submerged in the open water, or with roots embedded in the wet soil and flowers emerging into the open air; or in the various marginal areas, where the soil remains waterlogged but the plants are not submerged at all.
There are many cases of species living part of their lives underwater and the remaining (adult) phase out of it. Examples include frogs, toads and newts, as well as dragon- and damselflies, all of whose larval stage is spent submerged in freshwater, with metamorphosis into the adult form resulting in the development of air breathing lungs to replace their gills, and a complete change in lifestyle. There are many types of invertebrate found in wetlands, in and above the water. Species such as the freshwater shrimp, water hog louse and the scarce crayfish have gills and cannot survive in the open air. Others, like the great diving beetle, backswimmer and great pond snail, live in the water but come to the surface to breathe. Not surprisingly, the cleaner the water, the more abundant the wildlife. Plants have a major role to play here, filtering out impurities and providing dissolved oxygen for the aquatic fauna to breathe.
Larger animals include freshwater fish, like the stickleback and bullhead in ponds and streams, as well as water voles (scarce, nationally) and (again, rarely) otters. Small mammals like wood mice and water shrews live in and around wetlands. Many birds are associated with wetlands, such as the moorhen, coot and heron all common sights around the Borough and country as a whole. Others include the colourful great crested grebe, mallard duck and Canada goose. Some bird species are associated with wetlands because of the plants that grow there, but never enter the water itself. These include the reed warbler and reed bunting, both of which find their food and nesting sites amongst stands of common reeds and other marginal plants.
Where there is wildlife, we find predators and wetlands are no exception. Hen harriers, kestrels and sparrow hawks can all be found hunting around marshes, reed beds and the like.
As with rivers, pollution causes problems. Dangerous chemicals can be disastrous for wetlands, potentially wiping out everything living there. Excessive nutrients are also detrimental to biodiversity, as the wetland is fertilised, the faster-growing plant species are favoured. This includes blooms of algae: tiny, single celled plants that grow in huge, dense colonies, which form light-excluding mats on the waters surface and restrict photosynthesis by the submerged, oxygen-producing plants below. When the algal bloom inevitably dies, it decomposes and robs the water of oxygen still further. Not surprisingly, with little oxygen and few remaining plants in the water, prospects are bleak for the resident fauna. Over time, if such nutrient flushes occur regularly, a wetland once vibrant with life can turn into little more than a stagnant swamp.
Examples of wetlands in Redcar and Cleveland include Eston Mire and Moordale Bog on Eston Moor, and Guisborough Forest and Walkway's linear lake and reed beds.