Mirtoviški potok (Mirtoviči stream) is a nature reserve in the municipality of Osilnica, famous for its exceptional beauty and diversity of flora and fauna. It originates below Krempa in the middle of a hilly forest and represents one of the few preserved areas of natural heritage of extraordinary geomorphological forms, hydrological and biotope features. The karst spring gives the stream an exceptional nature conservation significance. The affluent "Modri ​​poh" is especially rich in waterfalls, pools, tubs and gutters, and crabs also live in it. The spring of the stream is located in an idyllic location and is surrounded by moss-covered rocks.

The stream used to run many mills and a sawmill, but today it runs a small hydroelectric power plant downstream.

A path from the road between Petrina and Osilnica leads to Mirtoviški potok, which starts right before the village of Mirtoviči. You can park your car at a rest area, and then continue on foot along a nicely marked and arranged path to the spring, where you need a good hour of walking.