On 3 February 1825 a flood pierced a permanent opening, the so-called Agger Channel, in the north of the 13 km long and less than 1 km wide isthmus, the Agger Tange, which had until then linked Thy with the rest of Jutland. The western part of North Jutland lost its road connection with mainland Jutland, but the towns and harbours in the western part of the Limfjord could benefit from becoming directly accessible from the North Sea, to the dismay of Aalborg. From the 1840s the route became increasingly important, as Britain had opened for import of grain, and ships could return with British coal. However, the instability of Agger Channel made the towns of the western Limfjord look for a second option.