The first proposal for legally organised protection of some lakes was made in 1969. At the time, the Institute for the Protection of Monuments – Nova Gorica conducted an inventory and evaluation of the notable and most famous natural phenomena in the Postojna municipality. The task was an expert basis for the preparation of a proposal for conservation in accordance with the Protection of Cultural Monuments and Natural Sights Act (Protection of Cultural Monuments and Natural Sights Act, 1958, Official Gazette of the People’s Republic of Slovenia, 22) and the Urban Planning Act (Urban Planning Act, 1967, Official Gazette of the SRS, 16).
After two years, the proposal was adopted as the Ordinance on the Nature Conservation Monument for the Municipality of Postojna (Ordinance on the Nature Conservation Monument for the area of the Municipality of Postojna, 1971, Primorske novice news, Official announcements, 7). It provided for the protection of lakes on the basis of two value levels, namely:
- Nationally significant inanimate natural monuments of the II. class (Palško jezero Lake, Petelinjsko jezero Lake). The protection regime prohibited any form of injury or endangerment.
- Locally significant inanimate natural monuments of the III. class (intermittent karst lakes in the headwaters of the Pivka: Veliko and Malo Drskovško jezero Lakes, Veliko and Malo Zagorsko jezero Lakes, Parsko jezero Lake, Kalsko jezero Lake and Baško jezero Lake)..
Interventions were permitted under the protection regime with the consent of the competent nature conservation service (Ordinance on the nature protection monument order for the area of the Municipality of Postojna, 1971, Primorske novice news, Official announcements, 7).
Despite the legal regulation and the conservation regime imposed by it, some parts of the lakes were still used for military training. Military training, especially on Palško jezero Lake and Petelinjsko jezero Lake, caused new injuries and pollution.
LIn 1984, the Assembly of the Cultural Community of the Municipality of Postojna in accordance with the Natural and Cultural Heritage Act (Natural and Cultural Heritage Act, 1981, Official Gazette of the SRS, 1) adopted the Ordinance on the Proclamation of Cultural and Historical Monuments and Natural Sights in the Municipality of Postojna (Ordinance on the Proclamation of Cultural and Historical Monuments and Natural Sights in the Municipality of Postojna, 1984, Official announcements, 29).
The Ordinance, for which the Institute for the Conservation of Natural and Cultural Heritage Nova Gorica prepared the professional basis, is still in effect today.
Palško jezero Lake, Petelinjsko jezero Lake, Veliko and Malo Drskovško jezero Lakes have been declared natural monuments.
The conservation regime determines the preservation of the natural state and prohibits pollution.
The conservation regime, which was conducted mainly in the area of Petelinjsko jezero Lake and Palško jezero Lake, continued to be disregarded. Only the changes caused by the abandonment of farming are visible in the Veliko and Malo Drskovško jezero Lake, which means the cessation of regular mowing at the bottom and the overgrowth of the slopes.
Other lakes were designated as natural heritage under the law, with protection based on guidelines rather than prohibitions. Based on new findings, the inventory of the natural heritage of the municipalities of Postojna and Pivka meant the extension of protection to thirteen lakes (Cernatič-Gregorič and Gorkič, 2005).
Prior to the establishment of the Nature Park, the Pivka intermittent lakes were protected under the Nature Conservation Act (ZON, Ur.l.RS 96/2004), which establishes the system of protection of natural values and measures for biodiversity conservation in order to contribute to nature conservation. The Pivka intermittent lakes have a special legal status based on nature conservation regulations and are protected areas (ZON, Ur.l.RS 96/2004). Four lakes (Palško jezero Lake, Petelinjsko jezero Lake, Veliko and Malo Drskovško jezero Lake) are protected as natural monuments on the basis of the old legislation from 1984.
Veliko Zagorsko jezero Lake, Malo Zagorsko jezero Lake and Parsko jezero Lake have been proposed as natural monuments, but all other lakes are not adequately protected.