The landscape of Lake Oulujärvi is well worth seeing, with its unique waters, beaches and pine forests. The trails of the Hiking Area go through light pine forests and on sandy banks. You can find your own favourite spot for picnic and swimming on the long sandy beaches though there is no official swimming spot.
The Oulujärvi Hiking Area consists of land and water areas on the island of Manamansalo and on Niskanselkä part of Lake Oulujärvi. The islands of Ykspisto, Ylä-Mulkku and Kaarresalo and parts of Honkinen, Kuostonsaari and Jylhänniemi are included in the Hiking Area. The water areas make up 64,3 sq.km. of the surface area, and 14 sq.km. consists of the islands and mainland.
The special natural features of Manamansalo include the lichen-covered heaths, the steep shoreline of Lake Oulujärvi, and the many clear forest lakes popular as fishing places. Pikes (Esox lucius) and perch (Perca fluviatilis) live naturally in lakes. In addition, rainbow trouts (Oncorhynchus mykiss) have been planted in lake Särkinen.
Lake Oulujärvi is the fourth largest lake in Finland. It was under the continental ice sheet until about 9100 - 9400 years ago. The surface area of the lake ranges between 778 and 944 sq.km. because the water level is controlled. The average depth is 7 metres, and in the deepest places it is about 38 metres.
Lake Oulujärvi flows into the Gulf of Bothnia through Oulujoki River. It is connected to Lake Nuasjärvi via Kajaaninjoki River, and receives 87% of its water from the rivers Kiehimäjoki and Kajaaninjoki. The lake is part of the water system of Oulujoki River, and the waterways of Hyrynsalmi and Kuhmo. The open water areas Niskanselkä and Ärjänselkä of Lake Oulujärvi are Finland's largest continuous open water areas on a lake.
Many of the islets on the open water areas are rocky and barren, piled up by the ice, but most islands have sandy beaches. On the edges of the large open waters, there are sandy shallows, where the Brown Trout (Salmo trutta m. lacustris ) comes to feed.
Most of the forests in the hiking area are dry pine forests. On the islands, also spruce-mixedwood forests and older forests can be found. In the areas which are central to tourism and hiking, there are handsome pine forests and older planted forests. There are only very small areas where the forest is in its natural state. The most impressive old-growth forests can be found in Rapsunkangas and Jylhänniemi areas. Other forests in the hiking area are former landscape forests of Metsähallitus.
Oulujärvi Hiking Area is interestingly located in a transition area of both the flora and the fauna. It is the southernmost inland water area where the Arctic Tern (Sterna paradisaea) and the Common Redshank (Tringa totanus) nest. The Ruddy Turnstone (Arenaria interpres) is a sea bird which is not found on any other inland water areas but this one. The Great Cormorant (Phalacrocorax carbo), on its way to the Arctic Sea, can stop at Lake Oulujärvi and stay for the whole summer. Also the Caspian Tern (Sterna caspia ) has nested several times in the area.
Other bird species typical for the area include gulls, the Common Tern (Sterna hirundo), the Black-throated Diver (Gavia arctica), the Red-throated Diver (Gavia stellata) and the Red-breasted Merganser (Mergus serrator). The most common waders are the Common Sandpiper (Actitis hypoleucos), the Wood Sandpiper (Tringa glareola) and the Little Ringed Plover (Charadrius dubius). In the dry pine forest are found, for example, the Tree Pipit (Anthus trivialis), the Common Redstart (Phoenicurus phoenicurus), the Eurasian Cuckoo (Cuculus canorus) and the Mistle Thrush (Turdus viscivorus ).