A marsh is a grassy meadow that is strongly influenced by salt from the sea. This type of nature is abundant in Denmark, among other places. The flatlands along the river that run out by Leirvågen, are the municipalities' largest marsh. At spring tide, these flatlands are flooded underwater for several hundred metres in over land.
Herlandsnesjane, a four-kilometre long peninsula in Lake Storavatnet in the middle of Osterøy, is well known among botanists. Here lies an unusually large and diverse bog.
Lake Purkebolsvatnet is perhaps western Norway's largest sleeping city - for birds. They come in the thousands, usually in later summer and autumn. The barn swallows alone number 10 000 - 12 000 at their most numerous.