Tide gauge is an oceanographic instrument measuring changes of the sea level. Changes of the sea level play an important role in our environment changes especially at the coastal zone. Tide gauges are an important tool in order to determine trends in mean sea level and extreme conditions, which are linked to the climate change, tidal computation, geodetic applications, harbour operations and navigation. Thus, continuous monitoring of sea level changes is necessary. The Institute of oceanography, HCMR participates in the European ocean observatory through the POSEIDON system with the installation of two tide gauges in the framework of the HIMIOFoTs project.