Environmental conditions influence the condition and survival of organisms and may influence levels of activity, relative condition, and mortality rates. Temperature has a direct effect on energetic demands associated with activity and rest and temperature-mediated physiological rates. Most organisms operate within narrow tolerance thresholds for temperature. Exposure to conditions outside these thresholds may have deleterious effects on metabolic demands, energy retention, and physiological rates. Experimental trials are one tool that may provide insight to species-specific tolerance to elevated temperatures. We ran experimental trials to examine the effects of elevated temperature on Pacific sand lance (Ammodytes personatus), an important forage fish in the North Pacific. Fish were held in tank trials at ambient (11 °C) and elevated (18 °C) temperatures in tanks with and without sediment. Analyses compared the effect of increased sea temperature on activity level, condition, and mortality. Experimental trials also examined the influence of the presence/absence of sediment on behavior. To compare experimental results with conditions experienced in situ, we evaluated a comparison dataset from the Salish Sea that spanned the 2014-2016 marine heat wave in the North Pacific. Analysis of in situ data showed a reduction in condition of Pacific sand lance populations in the Salish Sea during the 2014-2016 period of anomalous warming, but also recovery. Experimental trials demonstrated the importance of both temperature and sediment. Elevated temperatures resulted in reduced activity, reduced condition, and increased mortality. Absence of sediment had a negative effect on fish condition and survival and interfered with behavior associated with estivation and winter dormancy. Results provide insight into energetics and mortality that might be associated with future marine heat waves and have application to parameterizing ecosystem models.