<P> Bogs occur where the water at the ground surface is acidic and low in nutrients . In some cases, the water is derived entirely from precipitation, in which case they are termed ombrotrophic (rain - fed). Water flowing out of bogs has a characteristic brown colour, which comes from dissolved peat tannins . In general, the low fertility and cool climate results in relatively slow plant growth, but decay is even slower owing to the saturated soil . Hence peat accumulates . Large areas of landscape can be covered many metres deep in peat . </P> <P> Bogs have distinctive assemblages of animal, fungal and plant species, and are of high importance for biodiversity, particularly in landscapes that are otherwise settled and farmed . </P> <P> Bogs are widely distributed in cold, temperate climes, mostly in boreal ecosystems in the Northern Hemisphere . The world's largest wetland is the peat bogs of the Western Siberian Lowlands in Russia, which cover more than a million square kilometres . Large peat bogs also occur in North America, particularly the Hudson Bay Lowland and the Mackenzie River Basin . They are less common in the Southern Hemisphere, with the largest being the Magellanic moorland, comprising some 44,000 square kilometres . Sphagnum bogs were widespread in northern Europe but have often been cleared and drained for agriculture . </P> <P> A 2014 expedition leaving from Itanga village, Republic of the Congo discovered a peat bog "as big as England" which stretches into neighboring Democratic Republic of Congo . </P>

Where has the water in the bog come from