Biržai Regional Park covers 14,659 hectares (36,220 acres) in northern Lithuania near its border with Latvia.

It was established in 1992 to preserve a distinctive karst landscape.

The park is notable for its sinkholes, created by the dissolution of the gypsum underlying its soil.

About 9,000 sinkholes have been identified; the most notable is the Karvės ola (Cow's Cave), which is about 20 meters deep.

[2] In 1998 the use of pesticides and fertilizers in the area was restricted.