Cetacean watching from tour boats has increased in recent years. However, short- and long-term impacts of this industry on the behavior and energetic expenditure of cetaceans have been documented. Although multiple studies have investigated the acoustic response of dolphins to marine tourism, there are several covariates that could also explain some of these results and should be considered simultaneously. Here, we investigated whether common bottlenose dolphins, Tursiops truncatus, inhabiting Walvis Bay, Namibia vary their whistle behavior in relation to boat presence, surface behavior and/or group composition. We detected an upward shift of up to 1.99 kHz in several whistle frequency parameters when dolphins were in the presence of one or more tour boats and the research vessel. No changes were demonstrated in the frequency range, number of inflection points or duration of whistles. Whistle occurrence and production rates increased when tour boats were present. High natural variation was detected in the whistle behavior of bottlenose dolphins over varying behavioral states and group composition. Anthropogenic impact in the form of marine tour boats can influence the vocal behavior of dolphins and such changes could have a long-term impact if they reduce the communication range of whistles or increase energy expenditure.