One of the world’s rarest types of bear has suffered a setback after three of the animals were found drowned in a water tank in the Apennine mountains of Italy.

Three Marsican bears – a mother and her two cubs - fell into the concrete tank and were unable to scramble up its steep-sided walls.

The criticially endangered Marsican bear (Ursus arctos marsicanus) is a sub-species of the Eurasian brown bear and is found only in the mountains of central Italy, with the population estimated to be less than 50.

“This is a serious loss which risks cancelling out efforts to reduce mortality rates and to have the highest possible number of females of reproductive age,” said Antonio Carrara, the head of the national park where the bears live.

The national park covers a vast area of mountains, valleys and forest bordering the central regions of Abruzzo, Lazio and Molise.

Conservationists criticised the fact that the water tank was not protected by a fence, despite the fact that two other bears had drowned in the same tank in 2010.