Ceriagrion tenellum. Orthetrum coerulescens and Sympetrum danae have declined in eastern England during the present century and are now confined to a few localities in this region. The declines are due to the cessation of peat digging and to agricultural improvement. Measurements of habitat and counts of territorial males showed that the surviving isolated populations of these species are very small — total populations are probably of the order of hundreds or thousands only. To test the dispersal powers of acid water dragonflies acid water ponds were constructed at Wood Walton Fen, in a region which has lacked acid water for many decades. No acid water dragonflies have colonised these ponds during the last twelve years, although Aeshna juncea has visited them. Varying numbers of C. tenellum from Dorset were introduced to these ponds in 1974, 1975, 1979 and 1980. Only one of the introductions was successful, producing progeny which emerged two years later.. Its descendants did not survive. Some general conclusions about the conservation of dragonflies are drawn from this work.