Lockjärv nature reserve covers about 130 hectares beside the lake of the same name, around 20 kilometres northwest of Hassela. The reserve lies in Hassela Finnskog and spans Nordanstig and Hudiksvall municipalities in northern Hälsingland. It can be reached via a forest road that passes through the area, but there are no prepared facilities for outdoor recreation.

The forest bears traces of fire, including marks on living pines and dead wood, with old burned pine stumps and fallen trees scattered through the reserve. Near the lake, old pine forest includes trees estimated to be 250 to 300 years old. The reserve’s central area is a patchwork of old forest, wet ground, small bogs and damp spruce forest. Old willows and aspens grow in the wet forest.

The reserve is also a place to look for protected and uncommon species recorded in the area. These include the fungi tallticka, lappticka, rosenticka and doftticka, as well as the lichens dvärgbägarlav, lunglav and gelélavar. The nearby Gulliksberget nature reserve is about 350 metres away; Kvarnmyrorna nature reserve is about one kilometre to the north.