This taxon is currently regarded as valid for global Red List purposes, but was treated as a subpopulation of the Arctic charr, Salvelinus alpinus (Linnaeus 1758), for the most recent national assessment (Nunn et al. 2023).

The taxonomic status of Salvelinus subpopulations inhabiting the British Isles has not been definitively resolved since a series of endemic species were described between the mid-19^th and early 20^th centuries (Adams & Maitland 2007).

In the United Kingdom and Ireland, all of these taxa are treated as junior synonyms of the Arctic Charr, the name of which has been routinely applied to a widespread complex of polymorphic charr populations occurring throughout the Holarctic region (Jonsson & Jonsson 2001). However, there remains considerable uncertainty regarding the systematics of the genus across the majority of this range (Reist et al. 2013; Taylor 2016; Whiteley et al. 2019).

Members of this "Arctic Charr complex" exhibit bewildering subpopulation-scale ecological and morphological variability. When such divergence occurs within a single lake system, the different sympatric forms are often referred to as “morphs”, “morphotypes”, "ecomorphs" or "ecotypes" (Snorrason et al. 1994; Adams et al. 1998; Knudsen et al. 2006; Klemetsen 2010; Muir et al. 2016).

Some of these subpopulations and sympatric forms have over time been described as nominal species, including at least 15 from North America, around 30 from Europe and 12 from Siberia and the Far East. However, these taxa encompass only a small fraction of charr distribution and diversity, and there exist significant differences in opinion regarding which of them should be considered valid (Savvaitova 1995; Adams & Maitland 2007; Kottelat & Freyhof 2007; Klemetsen 2010; Whiteley et al. 2019).

With the above in mind, there is an emerging consensus that the striking genetic and phenotypic diversity exhibited by members of this genus cannot be adequately represented by a single accepted taxonomic system (Whiteley et al. 2019).

The Red List currently follows the nomenclature provided by Fricke et al. (2024), albeit a species-oriented conservation management approach is unlikely to prove appropriate for members of this genus (Barthelemy et al. 2023; also see 'Conservation').

Global and European regional assessment: Vulnerable (VU)
EU 27 regional assessment: Not Recorded

Lonsdale's Charr has an extremely restricted range (extent of occurrence (EOO) c. 7 km², area of occupancy (AOO) c. 4 km²), which meets the thresholds for the Critically Endangered category under Criterion B1 (EOO < 100 km²) and Criterion B2 (AOO < 10 km²). It is restricted to one location, but there is no indication of continuing decline or extreme fluctuations, hence it does not qualify for a threatened category under Criterion B.

There is no evidence of any population size reduction that would approach the threshold for Vulnerable under Criterion A (≥ 30% over the past ten years or three generations). The population size is unknown, precluding the use of Criterion C or Criterion D1, and there exists no quantitative analysis of extinction probability which would permit application of Criterion E.

Therefore, this species is assessed as Vulnerable under Criterion D2, based on its presence at one location which is threatened by habitat modification and climate change that could drive it to Critically Endangered or Extinct in a very short time period.

This species is endemic to the county of Cumbria in northwestern England, United Kingdom, where it is currently restricted to Haweswater Reservoir in the Eden River system.

A possibly conspecific subpopulation formerly inhabited the adjacent Lake Ullswater.

This species' current population size and trend have not been quantified. Overall abundance declined significantly between the 1970s-1990s, but indications of recovery have been reported since the mid-2000s (see 'Conservation').

Haweswater was formed after the last glacial period and is today an oligotrophic artificial reservoir that formerly comprised two smaller lakes, the outflow of which was dammed in 1939 to provide domestic water supply. The maximum water level is now c. 29 metres higher than before these engineering works were completed.

This species occupies the pelagic zone and is believed to feed predominantly on zooplankton.

Its life history has not been studied, but lacustrine congeners tend to spawn in autumn and deposit their eggs on clean gravel banks in shallow littoral or sublittoral zones. Mature individuals are likely to develop an intense epigamic colour pattern at this time. The extirpated Ullswater subpopulation is understood to have entered tributary streams to spawn.

The water level at Haweswater fluctuated significantly between the 1970s-1990s due to water abstraction for domestic supply (see 'Habitats and Ecology'). This is believed to have driven a decline in the resident subpopulation through dewatering of key sites during the spawning and egg incubation period. More recently, prolonged periods of drought have led to the water level being temporarily reduced by up to c. 60%.

In addition, predation by a Great Cormorant (Phalacrocorax carbo) breeding colony that settled at Haweswater during the early 1990s may have interfered with population recovery. The birds were managed for a period but these efforts were discontinued in 2008 (see 'Conservation').

Increasing water temperatures due to climate change represents an ongoing and future threat.

This species is not used or traded.

This species is included (as Salvelinus alpinus) as a priority species of conservation concern in the U.K. Post-2010 Biodiversity Framework.

Haweswater is located within the Lake District National Park protected area, which is also a UNESCO World Heritage Site.

Since the mid-1990s, management measures implemented at Haweswater have included attempts to manage the lake's water level in order to benefit native fishes.

The water utility company managing the lake trialled a number of bird scaring techniques between 1999-2004 in order to discourage further nesting by the Great Cormorant, among which frequent human visits to the nesting island proved to be the most successful. Between 2004-2006 a total of 29 Great Cormorants were also shot at the site, but after 2007 no further culling took place.

This species is not currently recognised by the relevant authorities in England or the United Kingdom, where it is treated as a subpopulation of the Arctic Charr (Salvelinus alpinus). The taxonomy of Eurasian charrs is in need of review (see 'Taxonomic Notes'), and it has been widely recommended that their conservation management must be considered independent of their systematic classification. Each subpopulation should therefore be assessed individually, taking into account its evolutionary and genetic significance coupled with the ongoing population trend and threats to result in a priority ranking permitting the effective allocation of conservation resources through the development of site-specific, catchment-scale management plans. Sympatric morphological forms should also be managed separately, depending on their respective habitat preferences, diets and life histories. The abundance trends of many subpopulations remain unknown, and their individual assessments should ideally form the basis of future research efforts in order to ensure appropriate prioritisation. In practice, such efforts should ideally be coordinated at local, national or regional scales.