Conservation of pool frog

The pool frog (Pelophylax lessonae) is one of Sweden's rarest amphibians. The species has been legally protected since 1986 and is protected under Swedish species protection legislation. Despite this, its population has declined dramatically, mainly because many of its habitats have disappeared or changed. Drainage, overgrown wetlands and changes to the forest landscape have caused many of the small, warm, fish-free ponds that the pool frog depends on to disappear or no longer provide suitable conditions.

Today, the pool frog survives in only a few ponds in Uppland and in a small number of forest ponds in north-eastern Kalmar County and south-eastern Östergötland County. The populations in Kalmar and Östergötland are particularly valuable because they have survived since the period following the last Ice Age, when the species was much more widespread in Sweden. Over the past centuries, the pool frog has disappeared from many of its former habitats.

In Östergötland, Lindalsgölen was long considered the most important site for the species. It supported an unusual population consisting of both pool frogs and edible frogs (Pelophylax esculentus), something that genetic studies showed to be extremely rare in Sweden. Despite efforts to improve the habitat and breed pool frogs outside their natural environment (ex situ) for later release, the frogs have failed to reproduce in recent years. The population is therefore now considered to be close to extinction, if it has not already disappeared.

In 2018, another unique population was discovered in Västervik Municipality. Genetic analyses showed that it consists of pure pool frogs, making it particularly valuable from a conservation perspective. These frogs also differ in appearance from the population in Uppland, having a much greener colouration. However, the population is very small, with fewer than 20 adult individuals, and faces a high risk of local extinction.

What we do at Nordens Ark

Nordens Ark is actively working to conserve the pool frog and secure the species' future in Sweden. Through many years of experience in keeping and breeding the species, we have developed extensive knowledge of its biology and ecological requirements.

Because the pool frog is highly threatened and the remaining populations are small, the County Administrative Boards of Kalmar and Östergötland have developed a joint reintroduction programme. The aim is to strengthen existing populations, create new breeding ponds and reintroduce the species to sites where it has previously disappeared. The work focuses particularly on the population in Kalmar County, which is of great importance for the species' future in Sweden. Using individuals from this population, we can both reinforce existing populations and reintroduce the pool frog to former habitats, such as Lindalsgölen.

In 2025, Nordens Ark began breeding pool frogs in its off-show breeding facility. A small number of frogs were collected from the population in Västervik Municipality without negatively affecting the wild population. These animals now form the foundation of the breeding population being established at Nordens Ark.

The tadpoles and young frogs bred at Nordens Ark will be used to reinforce existing populations and reintroduce the species to suitable habitats where it has previously occurred. In this way, we can strengthen small and vulnerable populations and improve the pool frog's chances of long-term survival.

News from the project – July 2026

In 2025, Nordens Ark launched a new conservation partnership with the County Administrative Boards of Kalmar and Östergötland to strengthen the genetically unique pool frog population in Kalmar County. During 2026, the first pool frogs bred at Nordens Ark were released into the wild to reinforce the existing population.

In collaboration with
County Administrative Board of Kalmar County
County Administrative Board of Östergötland County