Temperature avoidance behaviour of inanga,Galaxias maculatus, was studied in the laboratory using a two‐choice tank. The final preferred temperature of inanga is about 20°C but fish acclimatised to cooler temperatures (15 and 17°Q prefer warmer waters (up to 23 and 26°C, respectively). Fish acclimatised to temperatures of 15,17, and 20°C showed total avoidance at 29.5,31, and 31.5°C, respectively. Water temperature therefore is an important factor influencing upstream migration and distribution of inanga and thermal discharges can be disruptive.