Separated from the open sea of the Adriatic by a narrow sandy strip of "lidi", Venice's lagoon is a fragile natural ecosystem subject to tides, storms and silting. While the tides bring new life to the lagoon by renewing its water, they also threaten Venice, notably due to the acqua alta phenomenon, which the MOSE system seeks to regulate. Take a boat trip to fully get a feel of the lagoon's ambience, particularly beautiful at dawn and dusk, or when swathed in mist in autumn.