”Muhalnitsa” (Bulgarian: Мухалница) is a protected area in western Bulgaria, located at one kilometre south of the town of Botevgrad and at 63 km north-east of the capital Sofia.

The breeding season lasts only about two weeks, usually in the end of February or the beginning of March, depending on ambient temperature.

After the end of the breeding season, adult frogs return to the high parts of the mountain by land, covering approximately the same distances.

This leakage has probably influenced the water regime of the swamp, changing it from a temporary pond into a permanent one (with better conditions for the bulrush).

This would mean that in the following years the local common frog population will lose its main breeding site, and the unique migration will cease.

In 2017 the municipality of Botevgrad, together with zoologists from the Bulgarian Academy of Sciences, undertook a series of measures aimed at overcoming these threats by uprooting the bulrush and safe-proofing the road with animal passage pipes.