The influence of the critical latitude for tidal internal waves of frequency M2 (period 12.4 hours) is shown on the example of moored measurements. The critical latitude for internal waves M2 is 74.5° N. At this latitude, inertial and tidal M2 frequencies become equal, and internal tides cannot propagate over flat bottom. North of this latitude the temperature spectra reveal only the S2 peak (period 12.0 h), which means that vertical oscillations related to the internal waves with the M2 period are weak. Tidal internal waves in the Barents Sea are analyzed. The problem is solved based on a numerical model. Model parameters and generation conditions are determined from moored measurements. The input parameters are: stratification, tidal current velocities, ocean floor topography, and latitude. As a result of calculations and analysis, a map of the amplitudes of semidiurnal internal tidal waves in the Arctic seas was constructed. The maximum amplitudes of internal tidal waves occur over underwater slopes. Forced internal tides of high amplitude were revealed southwest of Spitsbergen. Very large amplitudes of internal tides were found in the Kara Gates Strait. Internal waves in this strait were studied on the basis of moored measurements and towed CTD-profilers in the scanning mode. The amplitudes of waves turned out to be extremely large. Their dynamics is close to similar waves in the Strait of Gibraltar. Waves with heights of up to 70 m are directed towards the Barents Sea. The countercurrent decreases the wavelength, and, consequently, the amplitude of the waves increases. The short-period internal waves under the ice and their influence on the fluctuations of the ice cover are investigated. When solving problems of internal waves, the boundary condition of a rigid lid is not completely justified. This is confirmed by measurements under the ice.