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This chapter discusses the management of open bodies of water and wetlands on seasonally or permanently waterlogged soil. It concentrates on freshwater habitats, but briefly discusses management of brackish habitats, such as coastal grazing marshes, where they form a continuum with freshwater ones. Topics covered include principles of manipulating water levels, water quality, methods of improving the value of deep water bodies (>1 m) and large, shallow (less than about 1 m) for wildlife; temporary pools, permanent ponds and water-filled ditches, rivers, swamps and fens, bogs, wet scrub, wet woodland, wet grasslands.

This introductory chapter begins by defining the meaning of temporary waters and discussing their biological importance. It underlines the confusion in terminology associated with this diverse group of freshwater habitats, and proposes a unified classification system. It concludes by emphasizing the key role of temporary waters in the global landscape.

About 12,000 of the 67,000 described species of crustaceans occur in fresh water. Crustaceans have colonized almost every type of freshwater environment in most parts of all continents. A common theme in marine-to-freshwater transitions is not only acquisition of osmoregulatory capabilities to cope with hyposalinity, but also optimizing reproductive strategies to cope with ecological and environmental variability. A key reproductive adaptation for fresh water is direct rather than extended planktonic development. Some groups, such as peracarids, were preadapted, already having direct development, whereas others, such as decapods, had to acquire it. Other crustaceans, such as branchiopods, are adapted not only to hyposalinity (and hypersalinity) but also to surviving in transient waters. Crustaceans have been colonizing fresh waters since the Middle Cambrian to Early Ordovician and have independently adapted to life in inland waters many times throughout geological history. The pattern and timing of invasions has shaped present-day distributions. Contemporary distributions and diversity of crustaceans in surface waters are surveyed in the context of their paleohistory. Different groups of crustaceans have very different current distributions that reflect the differential influence of different patterns of colonization, geological history, ecology, and the constraints (or benefits) of their evolutionary heritage.