The Neretva river system is one of the most biologically significant rivers in Europe. The Dinaric karst through which it flows supports around 25% of all freshwater fish species found on the entire European continent — a staggering concentration of biodiversity in a relatively small geographical area. The river and its tributaries harbour numerous species that exist nowhere else on Earth, and the wetlands of its lower reaches provide critical habitat for hundreds of thousands of migratory birds each year. Scientists who visited the upper Neretva during international research expeditions have repeatedly described the sheer abundance of life as something they had never encountered anywhere else in Europe. This natural wealth, however, is under serious threat from planned hydroelectric development, habitat loss, and the introduction of invasive species.
Fish — the endemic trout of the Neretva The Neretva is above all else a river of trout — and of trout species found nowhere else on Earth. The most celebrated is the Softmouth Trout (Salmothymus obtusirostris oxyrhynchus), known locally as mekousna pastrmka or mladica. This ancient species, the only representative of its entire genus in the Neretva basin, has inhabited these waters since before the last glaciation. It is characterised by a distinctively elongated snout, a small and unusually soft mouth, and relatively large scales — traits that make it immediately recognisable. It lives in schools in deeper, slower pools of the upper river, spawns in spring rather than autumn like most trout, and reaches an average weight of around 2 kilograms. Its best surviving populations are found in the upper Neretva upstream of Konjic — precisely the stretch most threatened by new dam projects.
The Marble Trout (Salmo marmoratus), known locally as glavatica, is the largest salmonid in the Adriatic basin and the second largest trout in Europe. Its extraordinary marbled pattern — irregular grey-green blotches over a silvery body — makes it one of the most visually striking freshwater fish on the continent. Large individuals have been caught in the Neretva weighing over 20 kilograms. It is a predatory species, feeding primarily on other fish, and it spawns on gravelly riverbed from November to January. Historically it was so common that fishermen along the Neretva caught giants exceeding 80 kilograms — accounts that today seem almost mythological but are documented in fishing literature from the early 20th century.
A third endemic, the Dentex Trout or Toothtrout (Salmo dentex), known locally as zubatak, is the most mysterious of the three — so poorly known that scientists still debate whether it represents a truly distinct species or a natural hybrid. It is named for the unusually prominent teeth covering its jaws, tongue, and palate. Beyond these three celebrated endemic trout, the Neretva basin is also home to the Adriatic Dace (Squalius svallize), several endemic karst minnow species (Phoxinellus spp.) found in isolated limestone poljes, the native Adriatic lineage of brown trout, grayling, and the European eel (Anguilla anguilla), which migrates from the Sargasso Sea to spend its adult life in the river before returning to the ocean to spawn and die.
Birds — Hutovo Blato and the river corridor
The Hutovo Blato Nature Park, fed by the waters of the Neretva's tributary Krupa, is the most important ornithological site in Bosnia and Herzegovina and one of the most significant bird reserves in the entire Mediterranean region. Listed on the Ramsar Convention since 2001 and recognised as a globally important bird habitat since 1998, it lies directly on the Adriatic Flyway — the great migratory route connecting northern and central Europe with Africa and Asia. Up to 10,000 birds can gather at the wetland at one time during peak migration, and over 240 species have been recorded in total. The great egret (Ardea alba) is considered the symbolic bird of the park, and local tradition holds that the nearby town of Čapljina takes its name from the Croatian word for egret — čaplja. Hutovo Blato also holds the only breeding colony of the pygmy cormorant (Microcarbo pygmaeus) in all of Herzegovina, where several hundred pairs nest annually.
Among the most spectacular species regularly seen in Hutovo Blato are the purple heron (Ardea purpurea), squacco heron (Ardeola ralloides), black-crowned night heron (Nycticorax nycticorax), glossy ibis (Plegadis falcinellus) with its iridescent emerald wings, Eurasian spoonbill, ferruginous duck, garganey, red-crested pochard, whiskered tern, and marsh harrier. The white-tailed eagle (Haliaeetus albicilla) nests in the park and is a sought-after sighting for visiting birdwatchers from across Europe. Along the upper Neretva and its canyon tributaries, the golden eagle (Aquila chrysaetos) breeds on the high canyon walls, the dipper (Cinclus cinclus) walks underwater along the riverbed searching for invertebrates, and the common kingfisher (Alcedo atthis) flashes electric blue along every clear tributary. The canyon cliffs at Vrelo Bune near Blagaj hold a spectacular colony of alpine swifts and Eurasian crag martins nesting directly in the rock face.
Reptiles and amphibians
The Neretva valley is one of the most important hotspots for reptile and amphibian diversity in Croatia and Bosnia and Herzegovina combined, with a total of 34 species recorded — 11 amphibians and 23 reptiles — the majority of which are listed on the IUCN Red List. The Balkan green lizard (Lacerta viridis) basks on sun-warmed rocks along the riverbanks throughout the middle and lower valley, while the nose-horned viper (Vipera ammodytes) inhabits the rocky slopes and dry stone walls above the river. The Aesculapian snake (Zamenis longissimus), one of the longest snakes in Europe, is a skilled climber found in the riparian woodland. The fire salamander (Salamandra salamandra) shelters under logs and rocks in the wetter canyon gorges of the upper river, emerging after rain to hunt earthworms and insects. The yellow-bellied toad (Bombina variegata) breeds in the shallow, sun-warmed pools along the river's edge. The most extraordinary amphibian of the entire Neretva karst system is the olm (Proteus anguinus), known in Croatian as čovječja ribica — literally "the human fish." This remarkable, fully aquatic cave salamander is blind, skin-coloured, and adapted entirely to life in the permanent darkness of subterranean karst waters. It has been recorded at numerous localities in and around the Neretva system and can live for up to 60 years. The olm is a living emblem of the Dinaric karst underground — an ecosystem hidden beneath the limestone that is as rich and fragile as the one above it.
Mammals
The forested and canyon walls surrounding the Neretva harbour a remarkable suite of large mammals that have disappeared from much of western Europe. Brown bears (Ursus arctos) roam the highland forests above the canyon, and grey wolves (Canis lupus) follow the river corridors at night. The Eurasian lynx (Lynx lynx), reintroduced to the Dinaric Alps in the 1970s, is occasionally recorded in the upper Neretva basin. The Eurasian otter (Lutra lutra), a sensitive indicator of clean water, is present along the clearer stretches of the river and its tributaries — its tracks in the riverbank mud a welcome sign of ecological health. Chamois (Rupicapra rupicapra) inhabit the near-vertical limestone walls of the Neretva canyon and the mountains of Prenj, Čvrsnica, and Čabulja above. Wild boar roam the riparian woodland of the lower valley, and red deer and roe deer frequent the forest edges at dusk. Bats are particularly diverse throughout the karst cave systems of the region, with numerous species using the river corridor as a nightly feeding route — their echolocation clicks barely audible over the rush of the current as they hawk for insects above the water in the darkness.
Invertebrates
The invertebrate fauna of the Neretva is extraordinarily rich and still incompletely known. Scientific expeditions to the upper river have described the sheer abundance of aquatic invertebrates as something rarely seen in Europe today — dense populations of stoneflies, mayflies, and caddisflies that indicate the first-class water quality of these still undammed reaches. These insects are not merely indicators; they are the foundation of the entire river food web, sustaining the trout, the dippers, and the kingfishers. Dragonflies and damselflies are abundant along the warmer lower reaches and at Hutovo Blato, where the calm water and dense reeds provide ideal breeding habitat. The white-clawed crayfish (Austropotamobius pallipes), now extinct or critically endangered across most of Europe due to a fungal disease spread by introduced North American crayfish, still survives in the cleaner tributaries of the Neretva basin. Butterflies are exceptionally diverse on the flowery limestone meadows above the canyon — the Neretva Science Week in 2022 discovered a moth species entirely new to science and named it Baeoura neretvaensis in honour of the river. Even the subterranean world beneath the karst holds its own invertebrate community — cave beetles, cave shrimps, and other stygofauna adapted to the permanent darkness of the underground water table, many of them with ranges measured in single cave systems rather than entire countries.
A river under threat
Despite its extraordinary biodiversity, the Neretva is considered the most threatened river in Europe. Over 70 hydroelectric projects have been proposed or are under construction along the river and its tributaries. Dams block fish migration, convert wild river stretches into stagnant reservoirs, destroy spawning gravel beds, and fragment the connected habitat that endemic species depend on. The planned Ulog dam on the upper Neretva would flood one of the last free-flowing stretches where the Softmouth Trout still spawns in healthy numbers. International scientists, conservationists, and local communities are actively campaigning for the protection of the remaining wild sections — because once a river like the Neretva is lost, nothing can replace what it took millions of years to create.
Baldo Kosić and the Dubrovnik Natural History Museum
The Dubrovnik Natural History Museum traces its origins to 1872, when the Museo Patrio was established around a private collection assembled by pharmacist and ship owner Antun Dropac. Its transformation into a major scientific institution, however, is almost entirely the achievement of one remarkable man. Between 1882 and 1917, teacher, natural historian and taxidermist Baldo Kosić collected, determined and prepared an almost complete collection of fish of the Dubrovnik region, and did the same for birds — an extraordinary body of work spanning three and a half decades. Kosić lived from 1829 to 1918, reaching the age of 89, and his years of intensive work in the museum represent the most prolific period of growth the institution has ever known.
Among his most spectacular achievements was the preparation of a leatherback sea turtle — the first one ever recorded in the Adriatic — captured in September 1894 off the islet of Sv. Nikola near Budva in Montenegro. The male specimen measured 2.14 metres in length and weighed 500 kilograms, and it remains one of the most dramatic exhibits in the museum to this day. The collection also holds a Mediterranean monk seal, a thresher shark, a smooth hammerhead, and the head and tail of an enormous tuna caught at the end of the 19th century near Ston — all testament to the remarkable marine fauna that once inhabited the southern Adriatic in abundance. Among the birds prepared by Kosić, 79 species are on the Red List and 48 appear in the Red Book of Endangered Birds of Croatia — meaning his meticulous preparations now serve as irreplaceable historical records of species that have since vanished or become critically rare in the region. The museum is located at Androvićeva ul. 1 in Dubrovnik's old town and can be visited as part of the Dubrovnik Museums group.
The Natural History Museum in Metković
In the autumn of 1947, ornithologist Dragutin Rucner came to the Neretva valley for the first time and met with members of the local Hunting Club in Metković. Out of a shared love for birds, the idea was born of establishing an ornithological collection that would introduce the public to the richness of birdlife along the lower Neretva. The Hunting Club provided the funds for research, and in return, specimens were prepared through taxidermy. Years of systematic fieldwork followed from 1948 to 1953, covering all seasons and all habitats of the lower Neretva. What makes Rucner's story particularly remarkable is that he was not professionally a biologist — he was a musician. Yet his precision in distinguishing not only bird species but also males from females, and younger from older individuals, set a standard that professional ornithologists admired. The Ornithological Collection in Metković opened to the public in 1952 in the premises of the Hunting Club, initially consisting of 240 bird exhibits. Rucner continued visiting the Neretva valley throughout his life, permanently bound to its birds and its people.
The collection grew over the following decades into one of the largest ornithological collections in Europe. In 2016 it was rehoused in a state-of-the-art Natural History Museum, which retained the historic taxidermy exhibits while adding touch-screen information panels, recorded birdsong for each species, and — in a memorable touch — an arrivals board in the style of an airport departures display, listing the incoming "flights" of migratory birds to the Neretva valley according to season. The museum is located at Kralja Zvonimira 4, Metković, and is an essential visit for anyone interested in the extraordinary birdlife of the lower Neretva and Hutovo Blato.