Most of the North sea is on the European Continental shelf. On average, the depth is about 93 to 94 meters only. In the south it is very shallow, only 25 to 35 meters. In the north in the bathyal zone north of Shetland, this depth increases to between 100 and 200 metres. In the south, the depth is at most 50 metres. An exception to this is the Norwegian Trench. It is deepest there, with a depth of 725 metres. The most shallow part of it is a sand bank called Dogger Bank. In the southern part, there are many sand banks.