Stjuža is the only Slovenian sea lagoon. Today, the area of the lagoon is an important part of the Strunjan Stjuža Nature Reserve, which is included in the Natura 2000 network, primarily to protect habitat for waterfowl.
Stjuža (from the Italian chiusa, meaning ‘closed’) is the only Slovene lagoon.
The shoal formed through deposition of sediments by the Roja Stream, and after the construction of a dam, which artificially closed the bay over 400 years ago, the newly created lagoon remained connected with the sea only through a flow-through channel. As there are no water currents or major waves in it, the flow of water depends solely on high and low tides. Due to its shallowness (the average depth is 0.5 m), the water in the lagoon is subjected to rapid warming and cooling.
Before the 1950s, the aquaculture run in the lagoon exploited the animals’ spring migration into the warmer, shallow part of the sea, where food was abundant. Fish swam into the lagoon through the “fish gate” with no chance of return. With the water cooling down in autumn, the quantity of plant and animal organisms that the fish fed on became scarcer and the fish were ready to leave the lagoon, but were intercepted at the exit by fishermen.
One ton of fish were caught by this method annually, mainly mullet, seabass, gilt-head bream and eel, but this just wasn’t enough for the activity to survive at a time of modern fisheries and fish farms.
Today, the lagoon area is an important part of the Strunjan Stjuža Nature Reserve, falling within the Natura 2000 network, the primary objective of which is to preserve biodiversity by safeguarding the habitats of endangered plant and animal species that are relevant not only for Slovenia, but for the entire European Union.
The underwater meadow at the bottom of the lagoon is a true treasure trove of crustaceans, molluscs, fish and other animals. The lagoon's shallowness, abundance of food, reed-beds and other halophilous vegetation attract aquatic birds throughout the year. Little egret (Egretta garzetta), Mediterranean gull (Ichthyaetus melanocephalus), Eurasian coot (Fulica atra) and other birds look here for food, shelter or a nesting site.
For more extensive information on birds, check out the DOPPS-BirdLife Slovenia website: http://www.ptice.si/.
Among non-native invasive species that can be found here, the Japanese oyster (Crassostrea gigas) and the nudibranch ragged sea hare (Bursatella leachii) are the most common. The latter appears in particularly large numbers – up to as many as 10 per square meter – in particular spots of the lagoon.