1974 and revised on 17 August 1993. The protected area consists mainly of woodland and has been set aside primarily to capitalise on the opportunities it offers for swimming and recreation. There is, for example, a 75 metre wide bathing bay with an excellent sandy beach and sandy bottom. The reserve covers a land area of 25 hectares. 

Storm-damaged forest
In January 2019, Marum Nature Reserve was hit by the storm Alfrida. Many trees have fallen. To facilitate outdoor recreation, windfalls have been removed from the area and along trails, rootwads have been rolled back and leaning trees have been taken down.

In a storm-affected area, it is important not to:

•  climbing on piles of trees, the tree trunks may start moving,
•  walk under leaning or hanging trees, they can slip and fall down,
•  don't walk under rootwads, they can tip back.

Some rice has been left in the area for nature conservation purposes; this rice will eventually be broken down. The deeper tracks left by forestry machinery will also eventually be reduced. The tracks will not be repaired as this could cause major damage, for example in the form of leakage of heavy metals to Björköfjärden.

The forest in the Marum nature reserve has undergone a change since the storm. Larger gaps have been created, allowing more light to enter, which will eventually favour pine and deciduous trees. There will also be a more even age distribution of the trees and an increase in dead trees, which will favour many different species of birds and insects, for example.

Forest land with natural forest qualities
Most of the reserve's woodland is covered with a grand-dominated older coniferous forest, often with a significant element of hazel. Parts of the area's forests have been felled in modern times, but they still have some in common with more untouched natural forest. Older parts contain both unusual and rare plants and animals.

Old trees provide shelter and food
The old spruces in the reserve are home to a variety of insects and spiders. These in turn provide food for several of the most typical inhabitants of the coniferous forest. These include tits such as the pine tit, tufted tit and black tit, as well as tree creepers and kingfishers. On Marboö, the forest is relatively rich in fallen trees. There are good conditions for wood-living insects and fungi to grow and thrive here.

The small islet of Kattören is partly covered with deciduous trees. Kattören, like other small islets out on the bays, is much sought after by seabirds as a nesting site. Here they will hopefully be left alone from disturbing foxes and people.

Leafy headland that invites you to swim
The southern tip of Marboö, Fredagsören, differs from the rest of the area. The headland is more open and the heaths are dominated by deciduous trees, especially ash, rowan and alder. Several of the older ash trees bear clear traces of pollarding, which indicates that the inhabitants of the village used to come here to harvest winter fodder for their animals. The western shore towards Björköfjärden is rocky and very inviting for swimming.

An area for outdoor recreation
The motive behind the creation of the nature reserve is to preserve and manage an area for outdoor recreation. This is done, among other things, by managing the sandy beach at Marum. The forest within the nature reserve will be managed in a way that is attractive to outdoor recreation. The island of Kattören will be preserved as a nesting place for seabirds.

Nature type: coast, sea and archipelago, forest
Available here: bathing area, paths