The purpose of this study was to assess the effect of temperature on the sensitivity of mixed age adult Daphnia pulex to a simulated cooling tower blowdown and a simulated refinery effluent. In addition, the metabolic rate compensation capability of Daphnia exposed to temperature was determined. An artificial refinery mixture (ARM) simulated the 1977 guidelines promulgated by EPA. Components of the ARM in mg were: ammonia (10), chromium (0.25), oil (10), phenol (0.1), sulfide (0.17) and suspended solids (20). Components of the simulated blowdown mixture (SBM) in mg 𝓁⁻¹ were: zinc (2), phosphate (25), chromate (15), sulfate (824) and boron (0.5). After 72 hours at 20 C and 120 hours at 10 C, the median apparent threshold LC50s of the SBM were 0.045 at 10 C and 0.026 at 20 C. Similarly, threshold LC50s of the ARM were 0.106 at 10 C and 0.016 at 20 C. Mixed age adult Daphnia were pre-exposed to sublethal levels (LC10) of the SBM and the ARM at both 10 and 20 C and then subjected to t's above ambient of 5.4, 8 and 12 C for one hour. One other group received sublethal exposure only and the controls were maintained only in dilution water. After exposure survival and the number of viable and nonviable young were assessed. Daphnia pre-exposed to both simulated effluents and short-term thermal shock had significantly more nonviable eggs and young. Survival of 20 C Daphnia pre-exposed to both simulated effluents and subjected to a 12 C thermal shock was significantly reduced. Reproductively immature Daphnia showed a noncompensatory temperature acclimation pattern. Several hypotheses were presented to explain the adaptive nature of the noncompensatory pattern observed. / Master of Science