Wetlands, lakes and rivers

Switzerland has been called the «reservoir of Europe» due to our country's abundance of water. Four large European rivers – Rhine, Rhone, Inn and Ticino – begin here and flow into three different oceans. All waterbodies combined occupy 1769 km², or 4.3 % of the country's territory. Standing waters (79 lakes of at least 50 ha and 6668 small lakes) cover an area of 1422 km², while watercourses account for 317 km². The dense and ramified network of rivers and streams has a total length of approximately 65 000 km.

While the surface area of lakes hardly changed between 1979–1985 and 2005–2009, watercourses showed a significant increase in area of almost 10 km² (2.9 %), mostly between 1992–1997 and 2005–2009. On the one hand, regulated rivers were given more space following flooding or as a result of targeted restoration measures; on the other hand, many culverted streams were daylighted. Significant increases in area took place in the eastern half of the country in particular, for example in the cantons of Aargau and Zurich.

Only half of all watercourses are in a semi-natural condition

While many waterbodies above 1200 m have largely retained their natural structure, the proportion of semi-natural, largely unaltered watercourses on the Central Plateau and in Alpine valleys below 600 m only just exceeds 50 %. On the Central Plateau, watercourses are culverted along 14 % of their length. Approximately 101 000 artificial obstacles over 50 cm high separate the streams into countless sections, impeding or preventing the migration of water organisms. Sudden discharge fluctuations caused by hydropower stations (hydropeaking) and insufficient residual water flow lead to a decline in biodiversity and in the population density of fish and small aquatic invertebrates (macrozoobenthos). Overall, 2700 km of watercourses (divided into 1300 residual flow sections) are affected by the use of hydropower. Of these, 28 % have very little residual flow or none at all; a further 40 % for which no data is available probably also have insufficient residual water. Areas with control structures to prevent flooding increased by almost 20 % from 1985 to 1997 and again by just over 10 % from 1997 to 2009. Finally, the water levels of almost all larger lakes in Switzerland (except Lake Constance and Walensee) are controlled by weirs. To prevent high water and flooding, the regulation of lake levels has intensified in recent years. This causes natural seasonal fluctuations in the water level (spring floods, low water levels in winter) to be even smaller on average, both in waterbodies with control structures and in seminatural ones, and leads to the disappearance of valuable periodically wet sites, such as marshes and alluvial zones.

In the shore and shallow-water zones of lakes, protection and exploitation interests are often in conflict. The shores of many Swiss lakes are built up with walls and harbours. On Lake Geneva, for example, only 3 % of the lake shore is in a natural condition. Bank protection structures diminish the ecologically valuable transition zones between water and land, drastically reducing the naturally high diversity of habitats and species in this zone. In addition, reed belts – particularly valuable from an ecological point of view – are unable to develop. A two- to fourfold increase in shallow-water zones would be necessary to preserve the biodiversity and the ecosystem services provided by our lake shores.

Need for river restorations

The Federal Act on the Protection of Waters, revised in 2011, proposes the ecological enhancement of rivers, streams and lake shores. Apart from providing adequate space for waterbodies, the plan envisages restorations and a reduction of the harmful effects of hydropower use. According to the Waters Protection Act, 4000 of the 15 000 km of watercourses that are in poor ecological condition are to be revitalised by the end of the 21st century. So far, some river sections have been restored and streams daylighted, but only about 15 km per year. Small and isolated projects generally only result in a marginal increase in biodiversity. Larger projects and restorations that establish connectivity between areas (e.g. Auenschutzpark Aargau, Thur river mouth ZH, Inn GR) are much more successful.

Improved water quality thanks to better legislation

The increased construction of chemical sewage treatment plants starting in the 1960s and the ban on phosphates in laundry detergents in 1986 greatly reduced the input of pollutants and nutrients from settlements in rivers and lakes. As phosphorus inputs diminished, the oxygen supply in the deep-water zones of many lakes gradually improved. However, in some lakes this is only achieved thanks to artificial aeration. In areas with intensive livestock farming, where large quantities of liquid manure are applied to farmland, some lakes still contain excessive levels of phosphorus; this is known as diffuse nutrient input because it cannot be centrally treated in sewage works. The data collected in small streams on small aquatic invertebrates (macrozoobenthos) show that many of these waterbodies are in poor biological condition. Certain pesticides from agriculture can seriously damage aquatic organisms and reduce biodiversity in waterbodies at a regional scale. Almost all pesticides used in agriculture are found in Swiss rivers. More than 104 different plant protection products and biocides were detected in five watercourses; the limits set out in the Waters Protection Ordinance were exceeded for 31 substances. Land-use analyses in the catchment areas of the studied watercourses revealed significant deficiencies in ecological quality, especially in intensively used settlement and agricultural areas.

Threats: warmer water temperature and invasive species

The water temperature in the Rhine in Basel has risen by more than 2 °C since the 1960s. Heated water discharged by cooling systems or wastewater treatment plants, but also climate change, have contributed to this development. The habitat conditions for aquatic organisms that are sensitive to increased temperature and for several species of fish have deteriorated as a result.

Invasive non-native animal and plant species enter our waterbodies in various ways. They are increasingly causing problems. In the Rhine in Basel, for example, native invertebrate species accounted for less than 5 % of individuals in 2004, while the remaining 95 % consisted of a few dominant invasive species. The percentage of alien species decreased again up until 2011–2012, as one invasive species that had reached extremely high densities in 2004 was replaced by the next one; however, non-native species still make up 65 % of the total number of individuals. The invasive zebra mussel was first detected in Lake Geneva in 1962 and rapidly colonised other lakes. It crowded out some native species but provided a new source of food for wintering waterbirds.

A plethora of problems for fens and raised bogs, despite constitutional protection

Mires have lost more than 90 % of their area in Switzerland since 1850, and most were destroyed before 1950. Although mires in Switzerland have been protected by the constitution since 1987, the quantitative and qualitative losses continue. For example, the area covered by mires decreased by another 10 % between 1997–2001 and 2002–2006, 25 % of mires became much drier, and woody plants further increased in 30 % of them 11. Ditches and other drainage structures are often not removed, disrupting the hydrological balance in mires and causing them to dry out. 55 % of the remaining mires are now managed at low intensity, which slows down or even prevents shrub encroachment, but in many sites, mire-friendly management practices are still a distant concept. Despite the mitigation of threats (drying out, increasing nutrient load, shrub encroachment), many mires are so small in size and so isolated that they lack the potential for regeneration and are unable to meet the requirements of characteristic species in terms of habitat size. In 2010, only five large mires of more than 500 ha existed in Switzerland (three in the Grande Cariçaie, the raised bog near Rothenthurm SZ, and the Robenhauser Riet ZH on Pfäffikersee). Moreover, 70 % of fens and 50 % of raised bogs do not have adequate buffer zones. Finally, the input of liquid manure and nitrogen from the air is still much too high in 84 % of fens and 100 % of raised bogs, causing the gradual deterioration of these sites.

Some examples of restored mires show that they have become damper and contain a larger amount of peat. To preserve the biodiversity and ecosystem services of mires, the surface area of raised bogs would have to be expanded by 190 % and that of fens by 170 %.

First steps have been taken, but much remains to be done

Although the waterbodies and wetlands under national protection only cover about 2 % of Swiss territory, they are essential for the conservation of biodiversity. Compared to other countries, however, only a small portion of these habitats is protected by national legislation in Switzerland.

The current plans for the restoration of waterbodies in Switzerland are a step in the right direction. Nevertheless, in many places, the designated space is insufficient for many species because there is nowhere to retreat in case of flooding. The adverse effects of hydropower use also need to be reduced.