Ecological and genetic interactions among conspecific populations play an important role in population viability, but these interactions are not always fully considered in strategies to recovery endangered taxa. The Southern Resident Killer Whales are a high-profile population listed as endangered by both the U.S. and Canada. Risks to the population are well known, and include insufficient prey, inbreeding depression, disturbance, and environmental contaminants. Here, we argue that a fifth factor–interactions with other sympatric killer whale populations–plays an under-appreciated role in the population’s current and potential status. Based on studies conducted over the past two decades, we illustrate that consumption of shared prey, behavioral interactions in shared habitat, and shared DNA through potential interbreeding with other populations will strongly influence the future trajectory of the Southern Resident Killer Whales.