Phytoplankton represents the first link in food chain, being responsible for nutrients assimilation and oxigen production through photosynthesis process. The fact that phytoplankton is sensitive to very small variations in ecological parameters, it is necessary that their analysis to be made in the shortest time possible. Taking into consideration the above mentioned, in situ measurements are the most recomended alternative to eliminate errors in prelevation, preservation and processing of samples. With an area of 394.30 km2, Razim lake is the largest lake in Romania. The lake is included in Ramsar convention regarding wetlands from 1991. The maximum depth measured in the date of sampling was 280 cm. The measurements of the chlorophyll concentrations were made near the bank, in order to find if the nearby land influences the water quality. Taxonomic groups differentiation can be made on the basis of relative fluorescence intensities, following sequential light excitation. In case of aquatic ecosystems, fishing and turism represent the most important anthropic presures and the main causes of ecological degradation. A total of 19 sampling points was set for measurements in Razim Lake, in October 2018. At the same time, the parameters like temperature, depth and transparency were measured. In Razim lake, phytoplankton recorded variation in concentrations between 3.12 μg/L (very good ecological status) and 60.9 μg/L (moderate ecological status). Acknowledgement: This work was supported by the project BSB27 - MONITOX funded by the Joint Operational Programme Black Sea Basin 2014-2020. The content of this publication is the sole responsibility of the authors and in no way reflect the views of the European Union.