Cook Inlet beluga whales (CIBs) are an endangered population residing in Cook Inlet, Alaska. We characterized the calling behavior of CIBs to improve our understanding of sounds produced by this population. Bottom‐moored hydrophones were deployed at Eagle Bay in summer 2009 and at Trading Bay in summer and winter 2009. CIB sounds were qualitatively analyzed and categorized as a whistle, pulsed call, or click train. A total of 4,097 calls were analyzed, and 66 unique whistle contours were identified. Whistles were quantitatively analyzed using a custom Matlab program. A chi‐square test showed the call category usage at Eagle Bay during summer 2009 and those at Trading Bay during summer 2009 and winter 2009–2010 differed significantly (P < 0.001). Pulsed calls were more common during summer months, and click trains within the frequency band (12.5 kHz) were more common in Eagle Bay. The variation in calling behavior suggests differences in habitat usage or in the surrounding environment, including background noise. With the proposed development projects in Cook Inlet and the potential increase in ambient noise level due to ocean acidification, it is important to understand how this endangered population uses sound, and what anthropogenic factors may influence that use.