Great interest from domestic and foreign tourists caused the migration of mountain frogs in the protected area of Muhalnitsa, which is located only one kilometre away from Botevgrad. The phenomenon, according to the scientists, is unique in the world and that is why it provokes the interest of amphibian lovers. Clips and photos of Ilias Strachinis, who came to Bulgaria to shoot the frogs Rana temporaria during their breeding season, caused a furore in the specialized group of Amphibians and Reptiles in Bulgaria.

According to a study done 50 years ago by Dr Vladimir Beshkov at the end of each winter, the senior representatives of the mountain frogs, wintering in the streams of the northern slope of Mount Bilo, head for the plain and overcome a distance of about 10 km in a few days. The mass arrival of thousands of frogs in the marsh in the Mouhlinitsa area probably began at the end of the last ice age, about 8000 ago, for propagation purposes.

The breeding period itself lasts only about two weeks, usually at the end of February and the beginning of March, depending on the temperatures. In the past years Botevgrad municipality organized a specialized Day of Frog Marsh in which, with interesting games and discussions, they introduced children and students with the interesting phenomenon. It was organized and drove to the swamp itself. The municipality has not yet announced whether the event will take place this year as well.