In some published literature, this species is treated as a subpopulation of the Bourget Whitefish (Coregonus lavaretus) or a member of the "Coregonus lavaretus species complex", and referred to by the English vernacular names "Common Whitefish" or "European Whitefish" (see below).

At the regional scale, the systematics of European ciscoes and whitefishes (Coregonus spp.) has been the subject of considerable debate since the turn of the 21^st century, with little indication of a definitive outcome.

It is widely accepted that non-anadromous members of this group have repeatedly undergone adaptive radiations in boreal, subarctic and perialpine lakes (Douglas et al. 1999, Østbye et al. 2005, Kahilainen and Østbye 2006, Harrod et al. 2010, Hudson et al. 2011).

Subpopulations inhabiting these systems largely diversified in the wake of the most recent glacial period 10,000-15,000 years ago. They are typified by parallel patterns of divergence in traits associated with foraging (i.e., gill raker counts, benthic vs. pelagic feeding ecology), physiology (i.e., growth rate, habitat depth partitioning) and reproductive ecology (i.e., reproductive timing and spawning habitat).

Up to six different sympatric forms sometimes referred to as “morphs”, "ecomorphs" or "ecotypes" have been recorded in perialpine lakes, and these radiations might be even more diverse in some large systems of northeastern Europe (Præbel et al. 2013, Doenz et al. 2018, Bitz‐Thorsen et al. 2020, Öhlund et al. 2020).

However, there exist significant differences in opinion regarding the taxonomic status of these forms.

In Northern Europe, including the United Kingdom, all except a handful of Irish subpopulations are usually regarded as belonging to two widely-distributed species; Coregonus albula (ciscoes) and C. lavaretus (whitefishes), with the latter also frequently referred to as the "Coregonus lavaretus species complex” (Etheridge et al. 2012, Wanke et al. 2017, Häkli et al. 2018, Crotti et al. 2020). Within this comparatively uniform taxonomic concept, the catch-all English vernacular name “Vendace” is typically used for C. albula while "Common Whitefish" or "European Whitefish" are applied to C. lavaretus.

Conversely, researchers and fisheries authorities based in Central Europe have tended to treat the different forms as distinct taxa, leading to the recognition of more than 60 species across the European region (Kottelat and Freyhof 2007, Selz et al. 2020, De-Kayne et al. 2022, Selz and Seehausen 2023). Under this diverse taxonomic concept, the name “Vendace” is restricted to its original usage for the United Kingdom endemic Coregonus vandesius and the native range of C. lavaretus is limited to its type locality of Lake Bourget in France.

In the absence of a region-wide consensus, the Red List continues to follow the taxonomy provided by Fricke et al. (2024).

Global and European regional assessment: Endangered (EN)
EU 27 regional assessment: Not Recorded

The Three Lakes Whitefish is natively endemic to three lakes in the upper Rhine River system, Switzerland. It has a restricted range (extent of occurrence (EOO) c. 356 km², area of occupancy (AOO) c. 256 km²), which meets the thresholds for the Endangered category under Criterion B1 (EOO < 5,000 km²) and Criterion B2 (< 500 km²). It is present at three locations, at two of which the quality of habitat is estimated to be declining and the number of mature individuals is inferred to be declining.

Therefore, this species is assessed as Endangered under Criterion B (B1ab(iii,v)+2ab(iii,v)).

This species is endemic to lakes Neuchâtel (fr. Lac de Neuchâtel; de. Neuenburgersee), Biel (fr. Lac de Bienne; de. Bielersee) and Morat (fr. Lac de Morat; de. Murtensee; extirpated from this lake during the early 20th century, but has since been reintroduced) in the upper Rhine River system, Switzerland.

It has been introduced to Lake Geneva (fr. Lac Léman; de. Genfersee), plus a number of other natural and artificial water bodies elsewhere in Switzerland and in France.

This species' population size is unknown, but it is understood to exceed the minimum threshold for Red List criteria (< 10,000 mature individuals). The current population trend has not been quantified.

It remains extant in lakes Neuchâtel and Biel. However, it is inferred to be declining in both systems based on recent fisheries data, which demonstrate a significant reduction in commercial landings since 2016.

It was extirpated from Lake Morat during the early 20^th century, but has since been reintroduced and is currently maintained by supplementary stocking with hatchery-reared individuals.

Lakes Biel, Neuchâtel and Morat are monomictic, perialpine, naturally oligotrophic lakes with maximum depths of 74, 152 and 45 metres, respectively. All three were formed after the last glacial period and are connected to one another via canalised river stretches.

In addition, Lake Biel has since 1878 been artificially linked to the Aare River, which was diverted though the manmade Aare-Hagneck Canal in order to control floods in the surrounding area. This engineering scheme significantly increased the size of the lake's catchment as well as delivery of sediment into the lake itself.

The lakes were each formerly inhabited by 2-3 whitefish species differing in traits related to feeding and reproductive ecology along depth gradients, among which a putatively undescribed profundal taxon was extirpated from lakes Biel and Neuchâtel during the 1970s. All native whitefish species were extirpated from Lake Morat during the first half of the 20^th century (see 'Threats').

A non-native subpopulation of the congeneric Bernese Whitefish (Coregonus albellus) today appears to be established in Lake Biel, having probably arrived from nearby Lake Thun (de. Thunersee) via the Aare-Hagneck Canal.

The Three Lakes Whitefish primarily occupies relatively shallow habitats in the benthopelagic zone, where it feeds on zoobenthos. Male individuals become sexually mature at age 3-4+, and females at age 5+. The annual reproductive period extends from November to December, when spawning takes place on well-washed littoral gravel beds. However, some individuals may continue to spawn at greater depths of up to 50 metres until February.

A rising human population in the catchments of lakes Neuchâtel, Morat and Biel after the turn of the 20^th century drove the development of industry and agriculture, which led to increasing pollution from domestic wastewater and runoff. The lakes subsequently entered a phase of eutrophication, which peaked in the 1970s and led to periodic stratification and anoxia in the hypolimnion. These events are likely to have driven recruitment failure and extinction of the sympatric profundal whitefish subpopulations in lakes Neuchâtel and Biel, and all native whitefishes in Lake Morat (see 'Habitat and Ecology') by significantly reducing the extent of available habitat and the abundance of zoobenthic resources.

A secondary outcome of such changes in the available range of spawning depths is the potential for overlap and increased gene flow between different whitefish species that were formerly segregated along depth gradients. This raises the possibility of speciation reversal and extinction events due to hybridisation and introgression, and such processes may have occurred to some extent in Lake Neuchâtel.

In Lake Biel, it is also plausible that the extent of suitable spawning habitat has progressively decreased since the late 19^th century due to increased sedimentation from the diverted Aare River, plus the dumping of waste materials from river modification projects. There also exists a plausible ongoing threat of competition with the non-native Bernese Whitefish (see 'Habitat and Ecology').

The non-native Three-Spined Stickleback (Gasterosteus aculeatus) is present in Lake Biel, and has been associated with recent whitefish declines in Lake Constance (fr. Lac de Constance; de. Bodensee) through competition for zooplankton resources and predation of early life stages. Although its abundance in Lake Biel is not currently considered to be problematic, it may represent a plausible future threat.

The invasive Quagga Mussel (Dreissena bugensis) was first recorded in Lake Neuchâtel during 2017, Lake Biel during 2019 and Lake Morat during 2021. Once established, this filter-feeding mollusc can drive driving significant food web alterations, including energy sources and pathways for pelagic fishes, due to its propensity to alter zooplankton abundance, community structure and composition.

Warming of the lakes due to climate change also constitutes a plausible ongoing and future threat.

This species is harvested commercially throughout its range, although both annual landings and the number of fishers have reduced considerably since the late 1980s. As of 2022, only 32 professional fishers were operating on Lake Neuchâtel, nine on Lake Biel and four on Lake Morat.

These outcomes have been partially attributed to the lakes' improved trophic status (see 'Conservation'), which is likely to have driven a natural reduction in productivity.

However, in Lake Neuchâtel annual landings averaged > 100 tonnes prior to 2016 but declined to < 25 tonnes from 2017-2020, and comparable declines have been noted in lakes Biel and Morat. There does not appear to have been a reduction in fishing effort during this period, and the precise driver(s) of this recent decline are unconfirmed (but see 'Threats').

This species is included (as Coregonus spp.) in Appendix III of the Bern Convention. There exist several protected areas around lakes Neuchâtel and Biel, some of which are listed as Ramsar Wetlands of International Importance.

Investment in wastewater treatment facilities and other policy-led measures since the 1980s has driven an improvement in water quality of all three lakes, with lakes Biel and Morat currently meso-oligotrophic and Lake Neuchâtel having returned to its natural oligotrophic status. However, productivity in Lake Morat remains relatively high despite the reduction in nutrient levels.

Annual closed fishing seasons are in place, and timed to coincide with the annual reproductive period. Translocation of non-native whitefishes has been prohibited throughout Switzerland since 1991.

It is recommended that future research should focus on confirming this species' current population trend and response to the ongoing threats.