The population of beluga whales in Cook Inlet, Alaska, is in decline, and since 2000 these whales have been under consideration for designation as "endangered" under the Endangered Species Act (and were placed on the list in October 2008, just before this article went to press). In order to study environmental and hydrodynamic impacts on the belugas' movements and survival in the unique habitat of the inlet, a three-dimensional ocean circulation and inundation model is combined with satellite-tracked beluga whale data. Model-whale data comparisons from two whale paths during a five-day period (September 17-21, 2000) covering 10 tidal cycles suggest that daily movements of belugas in the upper Cook Inlet follow propagation of the tides. Both whales took advantage of the twice-daily flood of mudflats by the very large tides (8-10 m range) to swim toward river mouths in shallow regions that are inaccessible during low tide. A significant correlation was found between whale locations and the model sea level. In the Knik Arm, north of Anchorage, ebbing and flooding rates are predictable, and the tracked whale followed the water velocity in direction and speed. However, in the Turnagain Arm, south of Anchorage, where a large change in topography along the arm causes nonlinear flooding and ebbing (including strong tidal bore currents with speeds up to 5 m s -1), the movement of the tracked whale was correlated only with the water level, not with the currents. The encouraging results from this study demonstrate the usefulness of the numerical model to help understand the belugas' behavior and will be followed by a more detailed study using a larger tracking data set and longer simulations. Such a study will help to evaluate potential impacts of future changes such as shoreline development, which may change flood regions and the belugas' accessibility to their feeding areas.