Adults measure 7–12 cm (2.8–4.7 in) and are usually dark grey to blue on the back and sides, with an orange belly and throat.

Living mainly in forested land habitats for most of the year, the adults migrate to puddles, ponds, lakes or similar water bodies for breeding.

The aquatic larvae grow up to 5 cm (2.0 in) in around three months before metamorphosing into terrestrial juvenile efts, which mature into adults at around three years.

Although still relatively common and classified as Least Concern on the IUCN Red List, alpine newt populations are decreasing and have locally gone extinct.

When genetic evidence showed that Triturus as then defined contained several unrelated lineages,[6][7][8] García-París and colleagues in 2004 split off the alpine newt as the monotypic genus Mesotriton,[9] which had been erected as a subgenus by Bolkay in 1928.

[10] However, the name Ichthyosaura had been introduced in 1801 by Sonnini de Manoncourt and Latreille for "Proteus tritonius", the larva of the alpine newt.

[3] Alpine newt populations have separated since the Early Miocene, around 20 million years ago, according to a molecular clock estimate by Recuero and colleagues.

[1][3][16] Higher temperatures during the Miocene or sea level oscillations may have separated early populations, leading to allopatric speciation, although admixture and introgression between lineages probably took place.

During their life in water, both sexes develop a tail fin, and males a low (up to 2.5 mm), smooth-edged crest on their back.

Males have a white band with black spots and a light blue flash running along the flanks from the cheeks to the tail.

They initially have only two small filaments (balancers), between the eyes and gills on each side of the head, which later disappear as the forelegs and then the hindlegs develop.

[15]: 214–215 [13]: 39–46 [1][16] Alpine newts have been deliberately introduced to parts of continental Europe, including within the boundaries of cities such as Bremen and Berlin.

The newts use logs, stones, leaf litter, burrows, construction waste or similar structures as hiding places.

These can range from shallow puddles over small ponds to larger, fish-free lakes or reservoirs and quiet parts of streams.

[15]: 215 On land, alpine newts are mainly nocturnal, hiding for most of the day and moving and feeding during the night or in the twilight.

They have been observed to climb up to 2 metres (6.6 ft) on vertical walls of basement ducts, where they hibernated, on wet nights.

[13]: 105–107  Migration to breeding sites occurs on sufficiently warm (above 5 °C) and humid nights and may be delayed or interrupted for several weeks in unfavourable conditions.

[13]: 89–90 Alpine newts tend to stay close to their breeding sites and only a small proportion, mainly juvenile efts, disperse to new habitats.

[13]: 122–128 The aquatic phase starts at snowmelt, from February in the lowlands to June at higher altitudes, while egg laying follows a few months later and can continue until August.

When she touches the base of his tail with her snout, he releases a sperm packet (spermatophore) and blocks the female's path so she picks it up with her cloaca.

[15]: 215  Experiments suggest that it is mainly male pheromones that trigger mating behaviour in females, while colour and other visual cues are less relevant.

[26] Threatened adult newts often take on a defensive position, where they expose the warning colour of their belly by bending backwards or raising their tail and secrete a milky substance.

[13]: 142  The chytridiomycosis-causing fungus Batrachochytrium dendrobatidis has been found in wild populations,[29] and the emerging B. salamandrivorans was lethal for alpine newts in laboratory experiments.

[30] Several subspecies of the alpine newt have been bred in captivity, including a population from Prokoško Lake in Bosnia that is now probably extinct in the wild.

[31][15]: 217 Because of its overall large range and populations that are not severely fragmented, the alpine newt was classified as Least Concern on the IUCN Red List in 2009.

The population trend, however, is "Decreasing", and the different geographic lineages, which may represent evolutionary significant units, have not been evaluated separately.

Introduction of fish, especially salmonids such as trout, and potentially crayfish is a significant threat that can eradicate populations from a breeding site.

In the Montenegrin karst region, populations have declined as ponds created for cattle and human use were abandoned over the last decades.

[2] In New Zealand, the risk of spreading chytridiomycosis to endemic frogs[23] has led to the introduced subspecies I. a. apuana being declared an "unwanted organism", and eradication being recommended.