The barene are the salt marshes of the Venice Lagoon: low islands of mud and salt-tolerant grass that flood at high tide and drain again at low. They cover about 70 square kilometres of the lagoon's 550, and roughly half the marsh surface recorded a century ago has gone (Madricardo et al., 2019).
What makes them unusual is how they stay alive. The marshes grow upward by catching silt and mud carried in by storm surges, which are the same events that trigger the MOSE flood barrier. Modelling of the whole lagoon for 2020 to 2023 found that closures reduced the flooded marsh area by an average of 27.5 per cent and marsh sediment accumulation by about 32 per cent, worth 2.6 millimetres a year of lost vertical growth against a relative sea-level rise of 4.4 millimetres a year (Michielotto et al., 2026).
This page explains what the barene are, why they depend on bad weather, how much of them Venice has already lost, what the gates cost them, the closure rule that could give most of it back, and where in the lagoon you can actually see them.
What are the barene in the Venice Lagoon?
A barena is a partially emerged flat of mud and sand, colonised by salt-tolerant vegetation, that sits high enough to be exposed at low water and low enough to be submerged when the tide rises. Seen from a vaporetto they look like fields of coarse grass cut by winding creeks, with a clean undercut edge where the tide has bitten into the bank.
The lagoon they sit in is microtidal and mixed semidiurnal, with a mean spring tidal range of 1 metre and maximum tidal oscillations of about 0.75 metres around mean sea level (Michielotto et al., 2026). That is a small range by ocean standards, which is exactly why the barene work: a marsh surface only needs to sit within a few tens of centimetres of mean sea level to be flooded regularly and drained completely.
Of the lagoon's 550 square kilometres, about 390 are open lagoon, including 40 square kilometres of tidal channels, 70 are salt marsh and 90 are fish farms (Madricardo et al., 2019). Average depth across the shallows is around 1 metre, while the deepest channels exceed 15 metres. The barene are therefore a small part of the surface and a disproportionate part of the ecology, holding the sediment, the nursery habitat and the birdlife.
Why salt marshes need storms to survive
A salt marsh is in a permanent race with the sea. If the surface gains height faster than relative sea level rises, the marsh persists; if it falls behind, it drowns and turns into open tidal flat. Height is gained by trapping mineral sediment out of the water that floods across it, so the marsh grows only when it is under water.
The Venice Lagoon has a particular problem with supply. All the major rivers that once fed it were diverted to the open sea between the fifteenth and seventeenth centuries to stop the lagoon silting up (Madricardo et al., 2019). No river sediment arrives any more, so accretion depends entirely on fine silt and mud being resuspended from the adjacent tidal flats and carried onto the marsh surface.
That resuspension happens when the water is deep, rough and moving, which means during storm surges. As the paper puts it, most of the sediments the marshes rely on "are delivered during storm-surge events, when suspended sediment concentrations are higher and inundation is deeper and longer" (Michielotto et al., 2026, p. 849). Those are the same conditions that trigger a MOSE closure. The storm that floods St Mark's Square is the storm that feeds the marshes, and the system built to stop the first also stops the second.
How much salt marsh Venice has already lost
The losses started long before MOSE. Comparison of sea-floor cartographies of successive ages shows a 50 per cent loss of salt marsh surface in the Venice Lagoon, alongside substantial deepening of the lagoon bed (Madricardo et al., 2019). For context, coastal wetlands worldwide have declined by about 25 per cent in the last two centuries, so the lagoon has lost marsh at roughly twice the global rate.
The causes are dated and mostly deliberate. River diversion ran from the fifteenth to the seventeenth century. Rigid sea defences on the barrier islands were built between 1740 and 1782, successive sets of jetties at the inlets between 1808 and 1927, and land reclamation for the industrial zone between 1927 and 1960. Groundwater and natural gas extraction caused about 9 centimetres of subsidence between 1930 and 1970. The dredging of the Canale dei Petroli, a deep tanker channel, between 1960 and 1970 let larger waves and stronger currents into the middle of a shallow basin (Madricardo et al., 2019).
Taken together these works pushed the lagoon into a negative sediment budget: more material leaves through the inlets than arrives. Artificial salt marshes have been built and stabilised since the 1990s to slow the trend, and the marshes that remain are still losing ground.
What the MOSE barrier does to the salt marshes
MOSE is 78 hollow flap gates across four barriers at the three lagoon inlets, filled with water so they lie flush with the seabed and raised by pumping air into them when the tide is forecast to exceed 1.10 metres above the Punta della Salute datum (Michielotto et al., 2026, p. 848). At that level about 12 per cent of the city floods, an extent managed with footbridges and raised pavements.
The first lagoon-wide accounting of the cost modelled 2020 to 2023 against a hypothetical lagoon with no barrier. Under current operation, the extent of flooded marsh area falls by an average of 27.5 per cent, equal to 1,784 hectares, and can drop by more than 75 per cent during individual events. Where flooding still happens it is shallower: mean inundation depth falls by 45 per cent, or 0.28 metres, with the sharpest effect in the central and southern lagoon (Michielotto et al., 2026, p. 849).
The sediment follows the water. Closures cut marsh sediment accumulation by about 32 per cent, which works out at 2.6 millimetres a year of lost vertical growth (Michielotto et al., 2026, p. 850). Relative sea level at Venice is rising at roughly 4.4 millimetres a year, so the marshes are being denied more than half the growth they need. The gates are raised only 1 to 2 per cent of the year, averaging 8.6 hours a closure and 146 hours a year, and the effect is already substantial (pp. 848, 850, 852).
Could the gates close less often and still keep Venice dry?
The same study tested an alternative closure rule the authors call AThOS, which raises the gates only when levels are projected to exceed safeguard thresholds at Venice (110 centimetres above the datum), Chioggia (130 centimetres) or Burano (110 centimetres), reopens them once seaward and lagoon levels match, and leaves at least two hours between consecutive closures.
The headline is that the barrier is currently used more than flood protection requires. Applied to 2020 to 2023, AThOS would have cut the number of closures by about 30 per cent, 20 closures in all, and the cumulative yearly duration of closures was on average 107.2 per cent longer than was necessary to protect the urbanised areas (Michielotto et al., 2026, p. 851). The authors attribute the over-closing to forecast uncertainty combined with a precautionary approach, noting that the wind climate and tidal forcing have not measurably changed. No formal operational protocol for MOSE is publicly available.
Under AThOS the loss of flooded marsh area falls from 27.5 per cent to 2.9 per cent, marsh sedimentation rises 19 per cent above current operation, and roughly 1.3 millimetres a year of accretion comes back (pp. 849, 850). Average lagoon water levels would sit about 0.17 metres higher than under current operation while staying below the safety thresholds. The fix is a timing rule rather than new hardware.
Where to see the barene
The northern lagoon holds the best surviving marshes and the easiest views of them. The public boat routes to Murano, Burano and Torcello run past long stretches of barena, and the channel markers, the bricole, show where the deep water ends and the marsh begins. The islands of Vignole and Sant'Erasmo sit in the middle of that ground and are served by the same network (Michielotto et al., 2026, p. 846).
One named example gives a sense of scale: the Palude di Cona, in the northern sector of the lagoon, is a shallow water area surrounded by salt marshes, 4 kilometres long, between 0.9 and 1.7 kilometres wide, with an average depth of 80 centimetres at mean tide (Cibic et al., 2025). Water that shallow explains why rowing boats and flat-bottomed craft still make sense out here and why a deep-draught vessel cannot follow.
Go at low water if you want to see the structure, because the creeks and the undercut banks are exposed. Go at high water if you want to understand the problem, because the marsh surface disappears. The ground itself is also sinking faster than the city: subsidence in the historic centre has run at 1 to 2 millimetres a year over the last 50 years, rising to 4 to 6 millimetres a year in poorly consolidated salt marshes (Lionello et al., 2026).
