Forests and Mires
The rock walls in both sides of Hepoköngäs gorge little by little become lower and less steep the further downstream one goes. There are herb-rich forests, streams, lush spruce bogs, fens and impressive flood forests along the slopes and edges of the river valley. Half of the area is covered in spruce dominant old growth forests, into which patches of herb-rich forests with lush deciduous trees bring variety. The other side of the area is made up if young, managed forest. Approximately one-tenth of the area is mire. A 150 hectare section of the area is part of the Natura 2000 network.
Birds and Vegetation
Birds common seen in the area include the Western Honey Buzzard (Pernis apivorus), the Western Capercaillies (Tetrao urogallus), the Black Woodpecker (Dryocopus martius), the Three-toed Woodpecker (Picoides tridactylus) and the Grey Partridge (Perdix perdix), which are all species which thrive in old-growth forests. A White-throated Dipper (Cinclus cinclus) has nested each year for quite some time right beside the waterfall and visitors often stay to watch it dive for fish to feed on in early spring.
The area's soil is nutrient rich and calciferous. This is evident in the area's vegetation, which includes for example, the Early Marsh-orchid (Dactylorhiza incarnata incarnata) and the Common Spotted Orchid (Dactylorhiza fuchsii) which are common in fen mires. Decayed deciduous trees add to the diversity of the area's species, by creating growth places for example for rare polyporus.
The River Heinijoki is part of the River Kiiminkijoki's headwaters. The River Kiiminkijoki is very rich in fish. The River Heinijoki has a natural brown trout population. Additionally fishers may encounter the grayling and the lake trout.