Extreme events are becoming more frequent due to anthropogenic climate change, posing serious concerns on societal and economic impacts and asking for mitigating strategies, as for Venice. Here, tidal gauge data from 4 stations of the Venice lagoon are used to characterize Extreme Sea Level (ESL) events by means of two dynamical indicators: the instantaneous dimension and the inverse persistence. A close connection is found between the occurrence of ESLs and the inverse persistence, while the instantaneous dimension informs us on the number of interfering factors contributing to the increase of sea level. We further examined the capability of the MoSE (Experimental Electromechanical Module), a safeguarding system recently put into operation, in mitigating extreme flooding events and its operational performances in relation with the values of the two dynamical indicators. We show that the two metrics can provide a valuable support to evaluate and inform operational lagoon forecasts.