This report gives an exposition of the applications Kalman filters and the related nonlinear filters offer when used in models describing tidal motion in seas and estuaries. In addition to methods that are generally used in this field, for example deterministic and black-box models, Kalman filters can provide significant contributions in particular situations. Although it is not our intention to claim that the use of Kalman filters is the most fruitful method for all problems, it will be shown that these filters exhibit some specific useful properties, not present in the above mentioned conventional methods. Before explaining the fundamental ideas of the Kalman filter and its advantages and disadvantages a short review will be given of other known methods.