No, by the official measure. The national environment institute ISPRA and the Veneto regional agency ARPAV have graded the lagoon's 11 natural water bodies under the EU Water Framework Directive since 2011. In the 2022 round none reached Good ecological status, 4 were in Poor and 7 in Moderate, against 2 in Good in 2011 (Cacciatore et al., 2025, p. 6).
That grade is read from the animals living in the mud, which is the standard way to judge a shallow coastal lagoon. Across 268 samples and 252 taxa collected between 2011 and 2022, taxa richness and abundance both fell significantly, and 2022 was the lowest year on record across the whole lagoon (Cacciatore et al., 2025, pp. 1, 17).
This page sets out what the monitoring agencies measure and what they have found: the official status round by round, what has gone from the lagoon floor, which pollution sources are named, how much water the tide trades with the Adriatic every day, what happens when the MOSE gates shut, and why green-brown water is not by itself a sign of dirt.
Is the Venice Lagoon clean?
The Water Framework Directive divides the Venice Lagoon into 11 natural water bodies and 3 heavily modified ones, grouped by salinity band and by how enclosed each one is (Cacciatore et al., 2025, p. 3). Since 2011 ISPRA and ARPAV have run a monitoring programme that surveys the invertebrates in the sediment at about 70 stations once every three years (the paper gives 77 stations in one place and 75 in another) and measures water chemistry seasonally at 30 sites every year (Cacciatore et al., 2025, p. 2).
Four rounds have been published, and the grades move in one direction. Counting the 11 natural water bodies: in 2011, 2 were in Good ecological status, 1 in Poor and the other 8 in Moderate. In 2014 the split was 1 Good, 1 Poor and 9 Moderate. In 2019, 3 were Good and 8 Moderate, with none in Poor. In 2022, no water body reached Good status, 4 were in Poor and 7 in Moderate, so the count in Good status across the four rounds runs 2, 1, 3, 0 (Cacciatore et al., 2025, p. 6).
Set against 2011, five water bodies had deteriorated by 2022: two that had been Good were Moderate, and three that had been Moderate were Poor (Cacciatore et al., 2025, p. 6). The authors' conclusion is a significant decline in both taxa richness and abundance over the twelve years, with 2022 the lowest biodiversity recorded across the entire lagoon, and the enclosed, less salty water bodies worse off than the ones the sea flushes (Cacciatore et al., 2025, p. 17).
- Good
- Moderate
- Poor
Show the figures
| Good | Moderate | Poor | |
|---|---|---|---|
| 2011 | 2 | 8 | 1 |
| 2014 | 1 | 9 | 1 |
| 2019 | 3 | 8 | 0 |
| 2022 | 0 | 7 | 4 |
What has disappeared from the lagoon floor
The index behind those grades counts the animals living in the sediment: worms, clams, crustaceans and their relatives. Between 2011 and 2022 some groups left the samples altogether, among them Clitellata, Hexapoda, Bryozoa, Copepoda, Nematoda and Pycnogonida, though the last four were only ever present in very small numbers. Others were halved or nearly lost: crustaceans, polychaete worms, bivalves, cnidarians, echinoderms, tunicates and ribbon worms. One group, the horseshoe worms (Phoronida), increased, while gastropods, decapods and chitons stayed roughly stable across the surveys (Cacciatore et al., 2025, p. 5).
The timing differs by animal. Bivalves were abundant in 2011 and 2014, then halved in 2019 and 2022. Gastropods rose in 2014 and 2019 and dropped sharply in 2022. Polychaete worms declined in 2014 and collapsed in 2022. Echinoderms peaked in 2014, at three times their 2011 and 2019 abundance, then fell sharply in 2022 (Cacciatore et al., 2025, p. 10).
Two arrivals are named as part of the explanation. The comb jelly Mnemiopsis leidyi, an invasive animal that eats zooplankton, has increased significantly in the lagoon since 2014, which makes it plausible that it has taken the floating larvae of the crustaceans, gastropods and bivalves that went missing after that year. The Atlantic blue crab began to proliferate in 2023, after this dataset closes, and it feeds on exactly these bivalves and worms (Cacciatore et al., 2025, p. 11). Eight species recorded in the last two campaigns were not on the Italian Society of Marine Biology checklist for the Adriatic and Mediterranean, six of them small crustaceans.
What pollutes the Venice Lagoon
The agencies name the sources: industrial discharges from Porto Marghera, sewage outfalls from the cities of Venice and Chioggia, harbour activities, agricultural and urban runoff, and atmospheric deposition (Cacciatore et al., 2025, p. 17). The scale behind that list is the catchment. The drainage basin covers about 1,850 square kilometres and holds about one million people, and twelve main tributaries deliver a mean of about 35.5 cubic metres of fresh water a second (Cibic et al., 2025, p. 3).
The nutrient picture has improved. Over the twelve years to 2022 dissolved inorganic nitrogen, ammonia, total dissolved phosphorus and dissolved organic carbon all fell significantly, while salinity rose significantly and dissolved oxygen fell; the water temperature trend was not statistically significant (Cacciatore et al., 2025, p. 11). The same study reports that trophic trends have improved recently but that eutrophic conditions persist in the inner parts of the lagoon, which it treats as one cause of the lower biodiversity in the enclosed water bodies fed by fresh water (Cacciatore et al., 2025, p. 17).
The mud tells a different story from the water. Sediment composition stayed largely unchanged across the four rounds apart from organic carbon, which nearly doubled between 2011 and 2022, and organic phosphorus, which rose almost fourfold between 2011 and 2019. The enclosed areas carried more fine sediment and more organic carbon than the parts under stronger marine influence (Cacciatore et al., 2025, p. 16).
Does the tide flush the lagoon clean?
To a large extent it does, and that is why a lagoon under this much pressure is not worse. The Venice Lagoon is shallow, averaging about one metre over 550 square kilometres, with shallow areas making up about 75 per cent of the surface, roughly 415 square kilometres. Its tides are the largest in the Mediterranean. In a single twelve-hour tidal cycle about 60 per cent of the lagoon's volume is exchanged with the north-western Adriatic through the three inlets at Lido, Malamocco and Chioggia. Every day the lagoon trades about 400 million cubic metres of water with the sea, against about 3.7 million cubic metres arriving from the rivers and the subsoil (Cibic et al., 2025, p. 3).
That daily rinse is uneven, which is the point. Salinity across the lagoon spans roughly 12 to 36 PSU, from close to sea water at the inlets down to a third of that near the river mouths (Sankara Narayanan et al., 2026, p. 10). The saltiest, most strongly exchanged water sits along the main tidal channels and at the three inlets, while the northern and inner western sectors stay freshest (Sankara Narayanan et al., 2026, p. 13).
The official grades follow the same map. Enclosed and less salty water bodies showed lower species richness than the saltier, better-flushed ones, and the decline between 2011 and 2022 held across every lagoon type (Cacciatore et al., 2025, p. 17).
Does closing the MOSE gates make the water worse?
The barrier is raised when the forecast tide is above 110 centimetres (Cibic et al., 2025, p. 2). To find out what a closure does to the water, a team floated 18 enclosures of about 0.8 cubic metres each in the Palude di Cona, a shallow and nutrient-rich area of the northern lagoon, and blocked sideways exchange for up to 48 hours. The first run was in the hottest week of July 2019, the second from 13 October 2020, when the real gates went up for a tide peak of 135 centimetres (Cibic et al., 2025, p. 4).
The expected result did not happen. No hypoxia developed inside the enclosures, even though the summer run fell in the second heatwave of 2019, and the autumn run showed only a slight fall in oxygen over 28 hours (Cibic et al., 2025, p. 14). What changed was the lagoon's metabolism. Suspended material settled out, ammonium in the water was 2.4 times higher after 24 hours, bacterial carbon production rose 86 per cent in the water column after 24 hours and 2.7 times in the surface sediment after only 4 hours, and the plankton shifted towards larger diatoms and dinoflagellates (Cibic et al., 2025, p. 18).
The experiment covers one to two days, which is the length of a normal closure. The gates have been held up that long in practice: from 4 to 6 December 2020 they stayed raised for 48 hours without a break in a strong southerly wind (Cibic et al., 2025, p. 14). What a far more frequent closure regime would do is not settled by this study.
Why the water looks dirty when the measurements do not say so
Colour is not a cleanliness reading. The lagoon is an optically complex system in which suspended sediment, freshwater inputs, tidal exchange and boat traffic all drive how clear the water is from place to place and hour to hour (Sankara Narayanan et al., 2026, p. 15). Measured reflectance peaks at around 560 to 580 nanometres, in the green to yellow part of the spectrum, which is why lagoon water reads green-brown rather than blue, and the river-fed inner lagoon is the most strongly coloured of all (Sankara Narayanan et al., 2026, p. 8).
Wind alone can turn it brown. In shallow sectors a strong wind lifts sediment off the bottom, and the satellite scene of 20 March 2019, taken under a south-westerly of 10.84 metres a second, shows a patch of exactly that in the central lagoon (Sankara Narayanan et al., 2026, p. 16). The water is also shallow enough that the seabed itself can contribute to the signal at low water or when the water clears (Sankara Narayanan et al., 2026, p. 16).
One chemical point does separate the lagoon from diluted sea water. Most lagoon samples sat outside or at the top of the reference range for marine dissolved organic matter, meaning the water carries a land signature from terrestrial inputs and local organic matter rather than reading as Adriatic water with fresh water added (Sankara Narayanan et al., 2026, p. 8).
