We studied physical and chemical conditions and the crustacean communities in temporary ponds in a military area in South Germany. All ponds were formed by driving of tanks. They were turbid, without higher aquatic plants but contained a unique crustacean community with endangered species such as the anostracan Branchipus schaefferi, the copepods Cyclops furcSfer and Metacylops minutus and the cladocerans Daphnia obtusa, Moina brachiata and Macrothrix hirsuticornis. Branchipus was only present in ponds which dried out and where driving occurred. Ponds which did not dry out and where driving events were rare or did not take place were devoid of Branchipus. Physical and chemical conditions were similar in ponds with and without Branchipus. Day-night fluctuations of temperature were up to 15 "C in summer. Conductivity was 200-300 pS cm-I, hardness ranged between 2 and 3.5 meq I-', alcalinity between 1 and 3 meq I-', pH between 7.5 and 9, dissolved phosphorus was <20 pg I-', concentration of nitrogen was <0.1 mg.1-l and oxygen saturation was >60% in the ponds except one pond where concentrations of nutrients and conductivity were somewhat higher. When driving of tanks had been stopped the number and size of the ponds decreased and their character changed. Branchipus schaefleri and other endangered species disappeared and more but common, benthic species such as the cladoceran Chydorus sphaericus and the copepods Megacyclops viridis and Eucyclops serrulatus gained importance. Branchipus schaeffiri is now close to extinction. Conductivity, hardness, alcalinity increased while pH decreased probably because algae were replaced by marsh plants. We conclude that driving of tanks raised clay particles, prevented the growth of higher aquatic vegetation and condensed the bottom sediments. All this was necessary to keep the ponds in an early stage of succession thus providing conditions necessary to maintain Branchipus.