Algae are critical to aquatic ecosystems and provide nutritious food to primary consumers due to their ability to synthesize essential fatty acids, in particular, long-chain polyunsaturated fatty acids (LC-PUFA). Aquatic ecosystems are experiencing increases in surface water temperatures as a result of anthropogenic climate change. Elevated water temperatures can potentially cause thermal stress for algae and disrupt critical physiological and biochemical mechanisms. As a response to temperature changes, fatty acid composition in membranes shifts in order to maintain membrane fluidity. To gain a better understanding of how elevated temperature influences fatty acid composition, growth experiments of a cosmopolitan freshwater diatom species, Navicula pelliculosa, were performed in a temperature-controlled laboratory environment. Diatom cultures were grown under different thermal regimes to examine the effects of temperature and time on LC-PUFA content. Temperature treatments were found to elicit an asymmetrical response in FA content, potentially resulting in reduced LC-PUFA availability.