New Red List: One in Three Native Freshwater Fish and Cyclostome Species in Hamburg Is Threatened

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Hamburg is not only a port city, but also a city of waterways. The Elbe, Alster, and Bille rivers, along with numerous streams, canals, tidal channels, and marsh waters, provide habitat for a diverse community of fishes and cyclostomes.

However, the new Red List of Hamburg’s Freshwater Fishes and Cyclostomes shows that many of these species are under pressure. Of the 47 native species assessed, 16—around 34%—are threatened. Including the two species that are extinct or missing and two that are extremely rare, a total of 20 species, or 42.6%, are on the Red List. Compared with the previous assessment, the classification of three species improved, while that of 14 deteriorated.

Changes to aquatic habitats and migration routes are particularly problematic: Many species depend on near-natural rivers and streams, suitable spawning grounds, or unobstructed connections between their different habitats.

The current Red List is the third edition for Hamburg. The first was published in 1991, followed by an updated edition in 2015. The new assessment is based on data recorded in the Hamburg species registry through December 31, 2024. The registry now contains around 124,000 records for fishes, including lampreys.

More than 50 established fish and Cyclostome species in Hamburg

The complete species list contains 72 species that have been recorded at some point within Hamburg’s city limits. Not all of them, however, are permanent members of Hamburg’s fauna. Marine species, for example, may occasionally travel far up the Elbe, while other fishes originate from stocking programs or have only been recorded sporadically.

A total of 53 species are considered established or probably established. These include six non-native species: goldfish (Carassius auratus), Prussian carp (Carassius gibelio), pumpkinseed (Lepomis gibbosus), round goby (Neogobius melanostomus), stone moroko (Pseudorasbora parva), and eastern mudminnow (Umbra pygmaea). Because these non-native species are excluded from the threat assessment, 47 indigenous or archaeobiotic species remain for assignment to a Red List category—44 fishes and three cyclostomes.

The current assessment is not based solely on how frequently a species is recorded at present. It considers four criteria: the current population status, the long-term population trend, the short-term population trend, and potential risk factors. The short-term trend covers the 20 years since 2005; records dating back to the mid-19th century are available in some cases for assessing long-term trends.

What exactly are Cyclostomes?

Alongside true fishes, the list also covers cyclostomes (Cyclostomata). In Hamburg, these include the European brook lamprey (Lampetra planeri), river lamprey (Lampetra fluviatilis), and sea lamprey (Petromyzon marinus).

Cyclostomes are jawless vertebrates and are zoologically distinguished from true fishes. Their elongated bodies resemble those of eels; lampreys are characterized by a circular, suction-cup-like mouth with horny teeth. During the parasitic phase of their lives, river and sea lampreys use it to attach themselves to other fishes and feed on their tissue and bodily fluids.

The European brook lamprey is not parasitic. The animals feed only during their larval phase, which lasts several years. After metamorphosis, adult European brook lampreys no longer eat. They reach sexual maturity, migrate to suitable spawning grounds, spawn in spring, and then die. The adult phase therefore lasts only a few months.

Hamburg Red List: 42.6% Extinct, threatened, or extremely rare

Of the 47 native species assessed, 23—just under half—are considered not threatened. Conversely, just over half of all species are assigned to either a Red List category or the Early Warning List—or cannot be assessed conclusively because of insufficient data.

• Extinct or missing: 2 species (4.3%)—European sturgeon (Acipenser sturio) and allis shad (Alosa alosa)
• Threatened with extinction: 1 species (2.1%)—Atlantic salmon (Salmo salar)
• Severely threatened: 7 species (14.9%)—twaite shad (Alosa fallax), zope (Ballerus ballerus), barbel (Barbus barbus), crucian carp (Carassius carassius), maraena whitefish (Coregonus maraena), burbot (Lota lota), and wels catfish (Silurus glanis)
• Threatened: 7 species (14.9%)—European eel (Anguilla anguilla), river lamprey (Lampetra fluviatilis), common dace (Leuciscus leuciscus), weatherfish (Misgurnus fossilis), European smelt (Osmerus eperlanus), sea lamprey (Petromyzon marinus), and brown trout (Salmo trutta)
• Threat of unknown extent: 1 species (2.1%)—the minnow Phoxinus morella
• Extremely rare: 2 species (4.3%)—common nase (Chondrostoma nasus) and vendace (Coregonus albula)
• Early Warning List: 3 species (6.4%)—white bream (Blicca bjoerkna), ide (Leuciscus idus), and European flounder (Platichthys flesus)
• Data insufficient: 1 species (2.1%)—vimba bream (Vimba vimba)
• Not threatened: 23 species (48.9%)—e.g., European perch (Perca fluviatilis), northern pike (Esox lucius), and tench (Tinca tinca)

In the narrower sense, 16 species, or 34%, are considered threatened. This includes only the categories “threatened with extinction,” “severely threatened,” “threatened,” and “threat of unknown extent.” The Red List as a whole also includes species that are extinct or missing and those that are extremely rare, so its scope is correspondingly broader.

A look beyond the state borders shows that freshwater fishes are under pressure not only in Hamburg: More than 40% of the species on the 2026 Red List of European Freshwater Fishes are considered threatened.

Salmon threatened with extinction—sturgeon and allis shad missing

The situation of the Atlantic salmon (Salmo salar) is particularly critical. It is the only species currently considered “threatened with extinction” in Hamburg. Within the city, it occurs almost exclusively in the Elbe. The river serves primarily as a migration corridor: Adult salmon pass through Hamburg on their way to spawning waters farther upstream, while juveniles—the so-called smolts—pass through the city on their way to the sea.

As recently as 1991, the Atlantic salmon was considered extinct or missing in Hamburg. In the decades that followed, records increased as a result of reintroduction programs in various tributaries of the Elbe. However, a large proportion of the animals recorded today probably originate from stocking; it is impossible to quantify how many salmon resulted from natural reproduction. Natural reproduction and self-sustaining populations have not yet been demonstrated. The species therefore remains threatened with extinction in Hamburg.

Because the Hamburg section of the Elbe forms an important migration route between the North Sea and spawning grounds in the Elbe catchment, Hamburg bears a high degree of responsibility for conserving the species. Above all, passage through the city must remain possible.

The situation is even worse for the European sturgeon (Acipenser sturio) and allis shad (Alosa alosa): Both are still considered extinct or missing in Hamburg. The last known sturgeon catch within the city dates from 1951; the most recent allis shad record dates to around 1900.

However, a European sturgeon reintroduction project has been underway in the Elbe catchment since 2008. Individual released animals have also been recorded within Hamburg since 2021. Successful natural reproduction in the Elbe has not yet been demonstrated. The species is therefore still listed as extinct or missing. Stocked fishes are generally excluded from this classification.

The situation is different for the allis shad: The species was already rare in the Elbe historically, which marked the northeastern edge of its natural range. No reintroduction to the Elbe is currently planned.

Since 2015: 14 deteriorations, 3 improvements

Compared with the 2015 Red List, the threat category changed for 17 of the 47 species assessed. Only 3 species received a more favorable classification: the European brook lamprey (Lampetra planeri), the European bullhead (Cottus gobio, called Groppe in the previous list), and the common nase (Chondrostoma nasus). By contrast, 14 species received a less favorable classification.

The species concerned are ide (Leuciscus idus), barbel (Barbus barbus), twaite shad (Alosa fallax), European flounder (Platichthys flesus), river lamprey (Lampetra fluviatilis), brown trout (Salmo trutta), white bream (Blicca bjoerkna), common dace (Leuciscus leuciscus), crucian carp (Carassius carassius), sea lamprey (Petromyzon marinus), burbot (Lota lota), European smelt (Osmerus eperlanus), wels catfish (Silurus glanis), and zope (Ballerus ballerus).

For the most part, the less favorable classifications cannot be explained solely by improved knowledge. For 10 of the 14 species whose status changed negatively, the authors primarily cite actual changes in the degree of threat as the cause; improved knowledge played a role for four species. Across all 17 category changes, 70.6% are due primarily to actual population changes, while 23.5% resulted from improved knowledge.

Long-term Trends and the past 20 years

Over the long term, 48.9% of species are assumed to have undergone a moderate to very severe decline or a decline of unknown extent. Only two species show a marked long-term increase, 15 are considered stable, and historical data are insufficient to assess five. However, older records are often incomplete, meaning that long-term trends can only be estimated roughly.

Over the past 20 years, 10 species showed a marked increase, while 15 populations remained stable. At the same time, another 15 species showed a moderate to very severe decline.

European brook lamprey and European bullhead show that conservation can work

The new Red List also documents some positive developments. These are particularly evident in the European brook lamprey (Lampetra planeri). On the 2015 Red List, the species was still considered severely threatened in Hamburg. Records have since increased significantly. In addition to the Seevekanal and Alster, the European brook lamprey is now once again found in tributaries such as the Bredenbek, Diekbek, and Tarpenbek. Its short-term population trend is therefore assessed as markedly increasing; on the 2026 Red List, the species is once again considered not threatened.

The European bullhead (Cottus gobio) has also improved. It was still on the Early Warning List in 2015, but is now likewise classified as not threatened. Current records come primarily from sandy lowland streams in the Alster system, from the Mellingbek, Bredenbek, and Seevekanal, and, to a lesser extent, from the upper Bille. The short-term population trend shows a marked improvement.

The Hamburg environmental authority attributes the positive development of the European brook lamprey and European bullhead in particular to restoration work, cleaner waters, and improved ecological connectivity. These two species thus demonstrate that measures to improve the ecological condition of rivers and streams can have measurable effects on their populations.

The situation of the common nase (Chondrostoma nasus) is less clear. It also received a more favorable classification than in 2015, but merely moved from “threat of unknown extent” to the category “extremely rare.” Only a very small number of records from the Elbe are available for recent years; according to the Red List, there is also no clear reason for the changed classification.

European smelt illustrates the problems facing the tidal Elbe

The European smelt (Osmerus eperlanus) is a characteristic anadromous migratory fish species of the tidal Elbe, the section of the river influenced by the tides. To reproduce, the animals migrate upstream from coastal waters into the Elbe. The European smelt was still considered not threatened in Hamburg in 2015; today it is classified as “threatened.”

Nevertheless, the European smelt is by no means rare. Measured by the number of individuals recorded in the species registry, it is by far the most abundant species: Around 1.76 million individuals are listed there for the period from mid-2013 to the end of 2024. However, the assessment also considers the breadth of a species’ distribution and the development of its populations. Within its main range in the Elbe and marsh waters, the current European smelt population is classified as only “moderately abundant.”

Monitoring surveys in the tidal Elbe show a severe population decline since 2014 for the European smelt. Although the latest catch surveys indicate possible stabilization, this is at a substantially lower level. Overall, at least a moderate decline is still assumed for the past 20 years.

The Red List identifies pressures including summer oxygen depletion in the tidal Elbe, the loss of shallow-water areas that serve as refuges and feeding and nursery habitats, and increased suspended sediment loads in spawning grounds. Potential harm from the withdrawal of Elbe water for cooling and, increasingly, heating purposes is another factor. Because the Elbe within Hamburg is a spawning and nursery area of supraregional importance for the European smelt, Hamburg bears a particularly high degree of responsibility for the species.

Hamburg bears particular responsibility for migratory fishes and lampreys

Its location on the tidal Elbe gives Hamburg significance far beyond the city limits. Many fishes and cyclostomes use rivers not as isolated habitats, but travel great distances between different habitats over the course of their lives.

Atlantic salmon, river lamprey, and sea lamprey are anadromous migratory species: They spend part of their lives at sea and migrate into rivers and streams to reproduce. By contrast, the European eel is catadromous—it grows up in inland waters and migrates to the sea to reproduce. Both forms are diadromous species that move between fresh and salt water during their lives. Other species migrate exclusively within freshwater systems; they are known as potamodromous.

For 15 of the 47 species assessed—almost one third—Hamburg bears a high or particularly high degree of responsibility for their occurrence in Germany. These include, in particular, species of the northern German lowlands, inhabitants of tide-influenced lower reaches of large rivers, and diadromous migratory species that must pass through Hamburg on their migrations. Overall, Hamburg bears a particularly high degree of responsibility for 6 species and a high degree of responsibility for 9.

Hamburg bears a particularly high degree of responsibility, for example, for the sea lamprey (Petromyzon marinus), for which the Elbe is an important migration route. For species including the Atlantic salmon (Salmo salar), European eel (Anguilla anguilla), twaite shad (Alosa fallax), crucian carp (Carassius carassius), and weatherfish (Misgurnus fossilis), Hamburg bears a high degree of responsibility.

What happens in Hamburg can have effects far upstream. Migration barriers or oxygen-depleted zones can temporarily or completely block passage through the tidal Elbe, thereby cutting more distant spawning and nursery areas off from the sea. The Red List notes that an oxygen-depleted zone in the Elbe could become an ecological migration barrier for diadromous species, thereby affecting the entire river catchment.

The condition of Hamburg’s waters therefore cannot be considered in isolation, especially for these species. The Red List of Germany’s Marine Fishes and Lampreys, published in 2025, also demonstrates that the protection of migratory species must not end at the boundary between river and sea.

Threats: engineered waters, migration barriers, and silted spawning grounds

Hamburg’s waters have been heavily shaped by human activity for centuries. Rivers and streams have been straightened, rerouted, deepened, or lined with reinforced banks. In the densely populated city, flood protection, shipping, and port use add further pressures. Such interventions can now be found in nearly all of Hamburg’s waters.

Engineered waters often lack natural structural diversity, including varied bed and bank areas, gravel, deadwood, and other features that create different flow conditions as well as spawning, feeding, and refuge habitats. Intensive maintenance can also be problematic: Ditch clearing can not only destroy habitats, but also kill fishes, large freshwater mussels, and other aquatic organisms directly.

Weirs, locks, sluice gates, and pumping stations are another problem. They can disrupt migration routes and isolate populations from one another. This affects not only diadromous species such as salmon or eel, but also fishes that move between different subhabitats within a river system. Impoundments also alter discharge, sediment transport, waterbody structure, and water quality, potentially impairing additional habitats. Dikes and dams can likewise break the connection between a river and its floodplain, making important spawning, feeding, and nursery areas inaccessible.

Fine sediments and inputs of substances are further pressures. When large quantities of fine sediment enter running waters, the particles settle into spaces between gravel and stones. This process, known as colmation, compacts the streambed and reduces the oxygen supply in the gravel interstices. This can be severe for species that lay their eggs in gravel: Reproductive success may decline substantially or fail altogether. In addition, the number of bottom-dwelling invertebrates that provide food for many fishes decreases.

Nutrients and pollutants place additional pressure on the waters. Heavy nutrient inputs in turn promote algal growth and can further degrade conditions on the riverbed. The 2025 Red List of Baden-Württemberg’s Fishes shows that such problems are not limited to Hamburg. It likewise documents marked deterioration among numerous native species.

Climate change is altering Hamburg’s waters

Climate change exacerbates many existing problems. Longer periods of heat and drought lead to higher water temperatures and more frequent low-water conditions. Smaller streams and headwaters may even dry up completely at times. This was already observed in numerous sections of Hamburg’s waterways during the dry years from 2018 to 2020.

Cold-water species are particularly affected, including burbot, trout, and other salmonids. Rising temperatures can shrink their suitable habitats and even cause populations to disappear locally.

In the tidal Elbe, rising water temperatures further worsen the already strained oxygen balance in Hamburg’s port area. During warm summer periods, oxygen depletion may intensify—with consequences for fishes and cyclostomes that depend on sufficiently oxygen-rich water.

The Red List identifies countermeasures including more shade from riparian trees and shrubs, deep refuges during low-water periods, improved waterway connectivity, and, where necessary, restrictions on water withdrawals and cooling-water discharges.

Aquatic conservation will shape Hamburg’s future

The new Red List presents a mixed picture: The European brook lamprey and European bullhead demonstrate that populations can recover when waters are restored and habitat conditions improved. At the same time, the three more favorable classifications since 2015 are offset by no fewer than 14 deteriorations.

Species such as the European smelt, twaite shad, burbot, and crucian carp also show that clean water alone is not enough. Rivers and streams need diverse structures and suitable spawning grounds and refuges, and they must remain connected. Another challenge is making them more resilient to heat, low water, and other consequences of climate change.

Hamburg therefore intends to continue implementing the European Water Framework Directive and to enhance the city’s aquatic network ecologically through the major nature conservation project Hamburg, deine Flussnatur. The implementation phase launched in 2026 comprises more than 500 planned measures across 38 waterways—including the creation of shallow-water zones, more natural watercourses, and ecological improvements to engineered banks. The Red List identifies improved waterbody structure, better ecological status, and the development of a habitat network as key project goals.

Red Lists show where action is particularly urgent, providing an important basis for conservation. For Hamburg, the message is clear: The city still supports a diverse community of fishes and cyclostomes, but many of its species are under pressure. And because the Elbe is both a migration route and a habitat for species from a much larger catchment, Hamburg’s responsibility does not end at the city limits.

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Sources

• Engler, O., & Mögeltönder-Löwenberg, S. (2026). Rote Liste der Süßwasserfische und Rundmäuler Hamburgs. 3rd ed. Free and Hanseatic City of Hamburg, Ministry for the Environment, Climate, Energy and Agriculture, Nature Conservation Department.
• Free and Hanseatic City of Hamburg, Ministry for the Environment, Climate, Energy and Agriculture (2026, August 25). Rote Liste der Fische 2026 – Erfolgreicher Naturschutz, aber auch starker Druck für Wanderfische wie Stint und Aal.
  https://www.hamburg.de/politik-und-verwaltung/behoerden/bukea/aktuelles/pressemeldungen/rote-liste-der-fische-2026-1211788
• NDR (2026, August 25). 50 Fischarten in Hamburg gesichtet – fast die Hälfte gefährdet.
  https://www.ndr.de/nachrichten/hamburg/50-fischarten-in-hamburg-gesichtet-fast-die-haelfte-gefaehrdet,fische-174.html