Brook trout (Salvelinus fontinalis) generally select areas of upwelling spring water for spawning under natural conditions. When presented with suitable gravel containing an artificially controlled aquifer of about 0.1% the area of a circular tank, female trout selected spawning sites that were either in close proximity to the upwelling water or adjacent to it in 21 of 22 trials. Average time lapse for completion of spawning was about 30 hours. Use of a tank several times larger than 1.9 m2would probably improve conditions for making more precise observations on discrimination of aquifers under laboratory conditions.