The composition of nests, built under standardized, static laboratory conditions by male three-spined sticklebacks Gasterosteus aculeatus from two rivers and two lakes in mid-Wales (U.K.) was quantified. After transfer to nesting tanks, fish from the rivers began building nests more quickly than fish from the lakes. The number of threads used in nest construction and the mass of substrate deposited co-varied, but there were no consistent population- or habitat-related differences in the aspects of nest composition. (C) 2008 The Authors Journal compilation (C) 2008 The Fisheries Society of the British Isles.