Due to the planned construction of Maasvlakte 2 the E.ON power plant on the Maasvlakte will not discharge its heated water into the North Sea anymore, but in the harbour basins itself. This together with a planned increase of the total amount of thermal discharges in the Maasvlakte area (power plants of EnecoGen and Electrabel, chemical industry etc.) will most probably lead to an increase of the water temperature within the harbour basins, which can lead to economical, legal and ecological consequences. In cooperation with the Port of Rotterdam and Deltares, this master thesis aimed to give an answer to the amount of increase of water temperature due to the planned thermal discharges, its consequences and measures to reduce this increase of temperature. With the use of some first estimates and a heat-balance there could be concluded that the increase of temperature is significant and that the movement of the tide together with the freshwater flux is the main mechanism for the netto heat flux out of the Maasvlakte area. Stratification has an important influence on the spreading of the heat plumes in the harbours. To give a more accurate prediction of the increase of water temperature at the mixing zone borders and at the intake locations (recirculation), the numerical hydrostatic model Delft3D-FLOW and the near-field model CORMIX are used. It is shown that the regulations will not be exceeded if the borders of the mixing zones are chosen close to the Beerkanaal. The predicted increase of temperature at the E.ON-intake will cause some economical losses. Replacing the intake at a greater depth or (even better) a variable intake near the water surface and bottom could be effective measures to reduce these losses. For a more drastic reduction of the increase of temperature in the harbour basins, relative expensive measures are needed. It is recommended to the Port of Rotterdam to place future thermal discharges as close as possible near the Beerkanaal or North Sea, and to study the ecological effects of the temperature rise in the Eastern Yangtzehaven.