Islands / Holmestrand / Kommersøya
An island of 0.7 km² in Sandebukta, most of it a nature reserve since 2006, on lime-rich Silurian bedrock that supports calcareous pine forest and species-rich dry meadows. The southern end is thick with fossils, and the island is an important recreation area.
The long, narrow island in the middle of Sandebukta is Kommersøya, about 2.7 kilometres end to end and only 400 metres across. From the east side you see pale pine forest gripping bleached limestone, and towards the southern tip the rock opens out in slabs full of Silurian fossils. Almost the whole island is a nature reserve.
Kommersøya nature reserve (2006). The boundaries and the rules are in Naturbase, and they are worth checking before you land anywhere outside the marked areas.
Own boat or kayak (public recreation area).
No scheduled boat comes here. You will have to find the nearest public quay yourself, and the rest is your own boat or a kayak. Check the wind and wave forecast before you set out; the open stretches in the outer fjord turn unpleasant in a fresh breeze.
The island has been called Kumarsøen and Marmorøya, and the second name says what people came here for: limestone and marble. Farming went on from the 1300s until around 1950. Through the 18th and 19th centuries the island was quarried for marble and burned for lime.
A lime works was built in the early 1890s. It went bankrupt in 1896 and was bought by a consortium. Christiania Portland Cementfabrik (CPC) bought its way in over four stages: 1897, 1899, 1908 and 1915. In 1915 CPC won state approval to build a cement factory on Kommersøya, but it was never built. The company had enough limestone from the rock at neighbouring Langøya, so the plant here stayed on the drawing board.
Christiania Eiendomsselskap, owned by Norcem after Norcem swallowed CPC in 1968, eventually sold most of the island to the municipalities of Sande and Holmestrand for public recreation. The company kept the right to quarry limestone later if it should ever be needed.
Kommersøya is a recreation area. People come to swim, to walk in the open pine forest and to look at the lime-loving flora. The ground is rich in lime, which gives calcareous pine forest and species-rich dry meadows, a combination that is rare along the fjord. The island holds one of the largest stands of yew in Norway, an estimated 10,000 plants of the slow-growing poisonous conifer. The southern end with the fossils is the most visited spot. In 2011 the municipalities of Sande and Holmestrand opened a cultural history trail together with Vestfoldmuseene, following the traces of farming and quarrying.
You get here by your own boat or kayak. There is no ferry. Almost the whole island was protected as Kommersøya nature reserve on 30 June 2006, covering some 480 hectares with the sea area included. The purpose is to preserve the calcareous pine forest, the dry meadows and the fossil-bearing rock. In a nature reserve, plants and animals are protected and motorised traffic on land is prohibited. Landing and swimming are allowed; use the marked paths and leave the vegetation standing. The exact rules on access are set out in the protection regulations, which should be checked before events or camping.
The old name Marmorøya was accurate labelling: marble really was quarried here in the 1700s, long before anyone thought about cement.
The southern end is one of the better fossil sites in the inner Oslofjord. The rock is from the uppermost Silurian, and it carries impressions of animals that lived on the sea floor more than 400 million years ago.
The cement factory that never came is one of the quieter industrial stories on the fjord. CPC had its permit in hand in 1915, but Langøya next door held so much limestone that the Kommersøya plant was never built. The island escaped and became a recreation area instead.
Farming lasted more than 600 years here, from the 1300s to around 1950, before it gave up.
Kommersøya holds yew by the thousand. Yew is among the slowest-growing trees in Norway, poisonous in every part except the red berry, and a single tree can live a thousand years. The lime in the ground supports an estimated 10,000 of them here.
Oslo Sea Experience passes Kommersøya on its private fjord trips from Tjuvholmen.
The Norwegian version notes which facts were taken from each source: Kommersøya på norsk.