Biržai Regional Park covers 14,659 hectares in northern Lithuania near its border with Latvia. It was established in 1992 to preserve a distinctive karst landscape. About 20% of its area is covered by forest.
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 Karves uola (Cow's Cave), which is about 20 meters deep.[1] In 1998 the use of pesticides and fertilizers in the area was restricted.