In order to better understand the cyanobacteria dynamics in fresh water bodies, a continuous in situ monitoring system was developed by PROLIPHYC project (funded by the French National Agency for Research ANR). It consists in a measurement buoy equipped with meteorological sensors and immersed probes to measure Chl-a, DO at 15-min time step and send them as a daily email to a database through GPRS protocol. This new monitoring approach offers several advantages over historical monitoring techniques: survey of remote sites, reduction of qualified personnel to perform sampling, reduction of overall cost of data collection and significant increase of quantity and quality of data set. In 2009, such a monitoring system was implemented in Lake Enghien (France), an urban lake (mean depth 1.3 m, 41 ha) frequently affected by blooms of the cyanobacterium Planktothrix agardhii. Collected data were used to input the coupled model DYRESM-CAEDYM in order to simulate the water temperature and the cyanobacteria biomass. Model calibration was performed with data collected during 15 days (1-16 June) and model validation was performed during a 5-month period (17 June -29 November). DYCD showed to be an appropriate model for simulating cyanobacteria dynamics in short and medium-term. The next step of our research consists in investigating the link between watershed changes and cyanobacteria dynamics. The study site is a tropical urban lake located in Brazil. Lake Pampulha (mean depth 5.0 m, 197 ha) inlet and outlet will be equipped with sensors to measure water temperature, turbidity and conductivity, flow and rainfall. Automatic samplers will collect water for analysis of quality parameters. Phytoplankton biomass and water temperature into the lake will be monitored by a measurement buoy fit out with a fluoroprobe and a CTD probe. This monitoring system is expected to provide lake response to new management strategies of the watershed.