ABSTRACT: Hillsborough Bay is a subembayment of Tampa Bay on the west-central coast of Florida. Beginning in December 1994, a series of reconnaissance measurements were made to define the probable maximum extent of the area where it could be possible to discern water transport associated with power station withdrawals/discharges. Routine field measurements in 1995-96 confirmed many conclusions previously derived from hydrodynamic models, but also provided much greater detail about the characteristics of water transport. Tidal action is the dominant force affecting water transport in lower Hillsborough Bay. The shipping channel that runs through the center of the estuary is a major conduit for water transport during flood and ebb tides. About one-third of the water transport for the southern segments of the routine measurement area moves through the shipping channel. Except during slack tide, water transport through the shipping channel is at least an order of magnitude greater than water transport for cooling-water withdrawals or discharges and, therefore, withdrawals or discharges at the Big Bend power station are unlikely to affect water-transport characteristics west of the main shipping channel. An east-west shipping channel, spoil islands, and a circulation-inducing cut interact to affect transport along the northern part of the routine measurement area. Along the southern part of the measurement area, shallower water causes transport to be more susceptible to effects from wind and bottom friction. Even when all four units of the Big Bend power station are operating, the effects of tide cause more than four times the volume of water used for power station cooling to move into and out of the routine measurement area. With each tide reversal, more than 25 times as much water enters or leaves Hillsborough Bay and more than 200 times as much water enters or leaves Tampa Bay than is circulated through the power station.