Fish Fauna 2022

Introduction

Water Bodies and Fish Communities

Berlin’s waterscape was shaped during the second stage of the Weichselian Glaciation, known as the Brandenburg Stage, which ended about 10,300 years ago. The Berlin Glacial Spillway is part of the Glogau-Baruth Glacial Spillway, which extends along the Weichselian end moraines of the Brandenburg Stage. Nestled within the North German Plain, Berlin’s waterscape is characterised by its prominent rivers, the Spree and the Havel. Together with their lake-like expansions, these rivers account for nearly two-thirds of Berlin’s water surface, totalling 5,952 hectares, or about 6.67 % of the city’s area. The Dahme and Spree rivers flow from the southeast into the Berlin Glacial Spillway, weaving through the city from east to west over 16.4 kilometres and 45.1 kilometres, respectively. Meanwhile, the Havel river enters from the north and meanders southward for 27.1 kilometres. The city’s largest water body is the lake-like expansion of the Unterhavel, spanning 1,175 hectares.

In addition to the rivers and canals that shape Berlin’s unique cityscape, there are 58 lakes larger than one hectare that lie at least partially within the city limits. Among these, the most remarkable are the fluvial lakes, featuring both river inflows and outflows. The Großer Müggelsee reigns as the largest lake, stretching across 766 hectares. In contrast, the Groß-Glienicker See stands as the sole substantial groundwater-fed lake. It is situated along Berlin’s southwestern border with Brandenburg, covering 667 hectares.

Small and very small water bodies dominate in terms of numbers. Berlin is home to a multitude of ponds, both artificial and natural, perennial and seasonal. It also features a number of quarry lakes and artificial rainwater retention basins. In total, 388 such water bodies are registered. They are joined by 316 drainage channels and ditches, some of which are piped, extending over a total length of more than 390 kilometres. These standing and flowing water bodies, small and very small in size, are predominantly managed and maintained by the city boroughs.

In Berlin, larger water bodies, such as rivers with catchment areas of more than 10 square kilometres and lakes exceeding 50 hectares, are subject to reporting under the European Water Framework Directive (WFD). Every six years, the European Commission requires updates on their ecological status and ecological potential, along with measures aimed at achieving a ‘good ecological status’. Therefore, current efforts and studies are primarily focused on this reduced network of lakes and rivers in Berlin that fall under this Directive.

Approximately 200 kilometres of Berlin’s flowing waters and ten lakes are monitored under the Water Framework Directive (WFD). Many of these flowing waters are manmade, such as canals and ditches. Type 21 ‘Flowing water discharging into a lake’ is the most common type of flowing water also among natural water bodies, due to the prevalence of fluvial lakes. Additionally, substantial portions fall into Type 15 ‘Sandy lowland river’, Type 14 ‘Sandy lowland stream’, and Type 11 ‘Humic stream’. Smaller areas at the mouths of tributaries are classified as Type 19 ‘Lowland water body’, while the Panke river, stretching from the Verteilerbauwerk, (tributary of the Nordgraben canal) to around Pankstraße, is classified as Type 12 ‘Gravelly lowland stream’. Some of these flowing waters transition between types, reflecting the natural longitudinal zonation of the rivers. For instance, the Spree changes type around the Elsenbrücke (at river km 22.05), shifting from a lowland river discharging into a lake to a sandy lowland river (SenUMVK 2021).

The lakes subject to reporting are mostly fluvial lakes with large catchment areas. They are classified as follows: the Großer Wannsee and Tegeler See are categorised as Type 10 ‘Stratified with a water residence time of more than 30 days’. Three other lakes fall into Type 11 ‘Unstratified with a water residence time of more than 30 days’, and a further four lakes are classified as Type 12 ‘Unstratified with a water residence time of 3 to 30 days’. The Groß-Glienicke See, a non-fluvial lake, also remains stratified during the summer, meaning its warm surface layer stays separate from the colder deep water below. It is therefore classified as a Type 10 lake. Unlike lakes with inflows and outflows, the water in the Groß-Glienicke See has a theoretical residence time of seven years (SenUMVK 2021).

The various types of flowing water are a lot more alike in their current morphological state, than the classification might suggest. Additionally, the reduced network of water bodies under the WFD overlooks the smaller water bodies. Similar to previous overviews of Berlin’s fish fauna, the present update is therefore based on a slightly different classification, which is, however, rather relevant when it comes to fish fauna. Flowing waters, canals, ditches, fluvial lakes, groundwater-fed lakes, and small standing water bodies of less than one hectare were classified based on their size, shape, connections, water sources, and potential as fish habitats.

The following section provides a brief overview of the main types of water bodies.

Flowing waters

The Spree, Havel, and Dahme are Berlin’s three major navigable rivers, collectively spanning an impressive total of 88.6 kilometres within the city’s boundaries. Among their key tributaries are the Fredersdorfer Mühlenfließ (3 km located in Berlin), the Neuenhagener Mühlenfließ (Erpe, 4.1 km), the Wuhle (15.7 km), the Panke (17.6 km), and the Tegeler Fließ (11.2 km), which discharges into the Tegeler See.

Berlin’s flowing waters are flow-regulated. The water levels of the Havel and the lower Spree, for instance, are controlled by the Brandenburg barrage. During low water periods, the water surface almost levels out, with a minimal 0.16 metre difference (0.002‰ gradient) between Spandau and Brandenburg. At medium water levels, this gradient increases slightly to 0.006‰ (0.35 m difference), and during flooding, it peaks at 0.014‰ (0.83 m). Further on, the Mühlendamm dam and Kleinmachnow lock on the Teltowkanal regulate water levels in the upper Spree of the city and the Dahme, keeping them nearly at equal height. Even as the Spree continues its journey to the Unterspreewald, it overcomes a modest total height difference of 14 metres (0.08‰). Finally, the Charlottenburg barrage regulates the flow of the Stadtspree, the central segment of the river in the city.

As a result, the average flow velocities in Berlin’s main flowing waters are relatively low, typically less than 10 centimetres per second. They can increase to over 0.5 metres per second during flooding with high discharge. In smaller tributaries, higher flow velocities are observed locally, particularly at former weir sites.
In terms of fish fauna, Berlin’s main flowing waters are categorised as belonging to the lower reaches of the rivers, specifically the Bleiregion (bream region). It is characterised by carp-like species such as the white bream, bream, bleak and roach as the predominant types. These types of water bodies are among the more species-rich habitats in the city, although the current average count of fish species (16) highlights significant deficits. In total, 38 of the fish species found in Berlin have been observed in this water body type, at least as individual specimens.

Canals

Canals are artificially constructed waterways designed to connect water bodies. As a result, they are characterised by long, straight sections with few shallows or bends. The banks are fortified and rather steep, presenting a uniform appearance with marginal deviations in width, depth, and design over long distances. Berlin’s navigable canals cover a total length of 80.1 kilometres and are primarily managed as federal waterways by the Wasserstraßen- und Schifffahrtsamt Berlin (WSA).

Moreover, Berlin’s canals serve a crucial dual purpose: they act as vital outlets for treated wastewater and as overflow channels for combined sewerage systems. In 2022, three sewage treatment plants, Stahnsdorf, Ruhleben (which operates only between April and September and is scheduled for permanent closure upon completion of the UV disinfection system), and Waßmannsdorf, thus discharged approximately 758,000 cubic metres of treated wastewater into the Teltowkanal per day, totalling about 277 million cubic metres for the entire year (SenStadt 2022). The Landwehrkanal is connected to 72 combined sewer overflows from the BWB (Berlin Waterworks) (Abgeordnetenhaus Berlin 2020). During intense rainfall, when pumping stations can no longer cope with the volume of water they receive, a mix of untreated sewage and rainwater (at a ratio of roughly 1:9) flows into the water bodies. From 2015 to 2019, there were between 3 and 33 instances annually, releasing anywhere from 550,000 cubic metres (2015) to 3.419 million cubic metres of combined sewage into the Landwehrkanal (Abgeordnetenhaus Berlin 2020).

Due to their monotonous structure and relatively high pollution levels, the canals are predominantly home to hardy fish species that can tolerate these conditions. On average, around 15 different fish species inhabit these canals, with more than 90 % consisting of roach and perch. In total, 25 of Berlin’s fish species have been recorded in the canals.

Ditches

The use of sewage farms for wastewater treatment began in 1876 and continued for a hundred years. The gradual increasing number of sewage farms prompted the creation of a dense network of inlet, outlet, and connecting ditches to service these fields. While most of the ditches dried up and were filled in after the sewage farms were permanently closed, there is still a large number of ditches that remain in Berlin to this day. These are small, minimally structured, and largely straight artificial flowing waters. About a quarter of the kilometres listed under ditches in Berlin’s water directory, particularly in densely built-up areas, are piped and uninhabitable for fish. Most ditches today carry very little water, with average discharges ranging from 10 to 250 litres per second. In years with little precipitation, they can sometimes dry up completely or in parts. When they are not shaded, these ditches develop dense vegetation such as reeds, reed canary grass, and true sedges, which can occupy the entire cross section of a ditch. As a result, regular clearing and mowing of vegetation are essential to maintain these ditches.

They provide a crucial habitat, for example, for the two native stickleback species, namely the three-spined stickleback and the nine-spined stickleback. On average, they host about five different fish species. Therefore, it is rather surprising that a total of 28 distinct fish species have been documented in these ditches.

Fluvial Lakes

Fluvial lakes are a unique feature of the lowland rivers in northern Germany. These expansive lake-like extensions formed along river basins due to the gentle gradients of the rivers and their valleys, combined with the relatively young development history of the landscape. These fluvial lakes blend the characteristics of standing water habitats with the influence of flowing water in their inflow and outflow areas. Connected to other fluvial lakes by the rivers that flow through them, these water bodies also link to traditional river stretches and their characteristic flowing water habitats. As a result, these fluvial lakes support not only typical standing water fish species but also migratory species that come for spawning and river fish that periodically use the lakes for foraging.

With the exception of the Tegeler See, the large fluvial lakes in Berlin are relatively shallow, ranging in average depth from 2.1 metres (Großer Zug) to 5.4 metres (Großer Wannsee). They warm up quickly and are rich in nutrients, providing excellent conditions for the typical fish species of the Bleiregion to thrive and find ample food resources.

Fluvial lakes are the most biodiverse water body type in Berlin, hosting an average of 21 and a total of 37 confirmed fish species.

Groundwater-fed lakes

Larger water bodies (>1 ha), primarily sustained by groundwater with minimal or no water inflow or outflow, are classified as groundwater-fed lakes. Unlike fluvial lakes, these have much lower water exchange rates and often retain water for several years or decades on average. In addition to naturally occurring groundwater-fed lakes, many have been artificially created. They are often remnants of former quarry lakes used for resource extraction. Despite their different origins, both natural (12 species) and artificial (11 species) groundwater-fed lakes vary very little in their average number of fish species. This similarity is attributed to both types being equally affected by human activities such as fish stocking and surrounding land use. The difference in their overall diversity was therefore rather surprising: artificial groundwater-fed lakes support 25 species, whereas natural ones are home to 33 species.

These groundwater-fed lakes provide ideal conditions for fish species that typically thrive in nutrient-rich, seasonally warm standing waters.

Small Standing Water Bodies

This category encompasses all standing water bodies smaller than 1 hectare, whether natural or artificial. Like the larger groundwater-fed lakes, these small water bodies are influenced by various factors, making further differentiation impractical. The types of small water bodies, their shoreline structures, and the surrounding land uses vary widely, ranging from fully concreted rainwater retention basins and artificial park ponds to silted quarry ponds, and natural remnant water bodies. As a result, a diverse array of 32 fish species has been documented in these environments.

Due to their small size, each water body typically supports only a limited number of fish species, averaging around five. Among these, common standing water species such as tench and rudd, but also roach and pike, are prevalent.

European Directives

Implementing directives from the Council of the European Union involves meeting complex requirements regarding the quality and collection of fish stock data. For instance, Council Directive 92/43/EEC of 21 May 1992, known as the ‘Habitats Directive’, focuses on the conservation of natural habitats and of wild fauna and flora (Official Journal L 206). This EU Directive also includes Annex II, which details ‘Animal and plant species of community interest whose conservation requires the designation of special areas of conservation’ (last amended by Directive 2006/105/EC of the Council of 20 November 2006). Among these, Annex II also lists four fish species currently found in Berlin: bitterling, asp, weatherfish and loach.

The European Water Framework Directive (WFD), established on 23 October 2000, was the first European regulation to use fish fauna as a biological element for assessing the ecological status of water bodies. The Directive’s approach for evaluating the ecological status of lakes and rivers is based on composition, abundance and age structure of the fish fauna as well as the presence of species sensitive to disturbances. The goal of the WFD was to achieve good ecological status for all surface waters, and good ecological potential for artificial and heavily modified water bodies by 2015. However, since these targets were not met by 2015, a second extension of the deadline to 2027 has already been adopted. Results from monitoring programmes under both the Habitats Directive and the WFD continue to inform the Environmental Atlas.