To some extent the presence of odonates may be taken as an indicator of ecosystem quality. Local faunal composition may be strongly affected by any change in water flow, turbidity, etc., or in aquatic or waterside vegetation.
Odonata are an order of aquatic palaeopterous insects. There are about 6500 extant species in just over 600 genera. Adult odonates are medium to large in size, often conspicuous and/or brightly colored insects and are aerial predators hunting by sight. They are usually found at or near fresh water, although some species roam widely and may be found far from their breeding sites. The larvae are predatory, aquatic and occur in all manner of inland waters. The greatest numbers of species are found at sites which offer a wide variety of microhabitats. The modern order of Odanata, is divided into two main suborders: Zygoptera (damselflies) and Anisoptera (dragonflies). The common name "dragonfly" is used for the whole order. More than one-half of all species are tropical but odonates of both major suborders occur in every faunal region except Antarctica. A third suborder, Anisozygoptera, largely known from fossils, is represented by one extant species in Japan and one in the Himalayas. Superfamily and family distributions in Odonata reflect ancient vicariance events such as the break-up of the southern continent Gondwana. Some genera and species are widespread. Others are highly local in distribution. Some families are restricted to cool streams or rivers, others to ponds or other still waters, and some to marshy places. The most species-rich and widespread family is the mainly tropical Libellulidae (Anisoptera). The most restricted is the monotypic Hemiphlebiidae.