Silkosia is the oldest reserve in the country, declared on 23 July 1931[1] in order to protect the evergreen bushes unique for Europe.

It encompasses part of the Veleka river catchment area with a territory of 389.6 ha or 3.896 km2.

[1] The terrain is various, in the lower parts there are predominantly swamp areas with typical Central European flora.

[2] In the wet valley rare species such as the strandzhan periwinkle, laurel, caucausian blueberry, common yew can be observed.

The most common flowers are the caucausian cowslip and the spring cyclamen which blossom in February and March.