Work ran from 1856 to 1861. The finished canal was 4.4 kilometres long, about 25 metres wide and 3 metres deep, running along the mainland west and southwest of the town so that vessels could slip past the shoals and come alongside Løgstør's merchant quarter. It was named for the reigning king, Frederik VII, and for four decades it did precisely what it was built to do. Several hundred ships used it each year at first; by the end of the nineteenth century the count was approaching three thousand vessels annually. For a town that had spent three hundred years being told it was too small and too shallow to matter, a royal canal delivering three thousand ships was vindication in engineering form.

The vindication did not last. A canal is a detour, and a detour is only worth taking while the direct route is impassable. Dredging technology improved through the late nineteenth century until it became practical to simply cut a navigable channel straight through the Løgstør Grunde themselves — shorter, wider, free, and requiring no locks or tolls. Ships took it. The canal closed to traffic in 1913, fifty-two years after it opened, defeated not by disaster but by the ordinary advance of the thing it had been built to avoid. It was not filled in. Preserved for its cultural value and formally protected in 1958, Frederik VII's Canal survives as a long green corridor of still water beside the fjord: one of the more legible monuments in Denmark to the risk of solving a problem instead of removing it.

Løgstør first appears in the written record in 1514, described as a fishing village. By 1523 it had a customs office, and through the sixteenth century it prospered — as Nibe did, further east — on the Limfjord herring markets. What it did not get was permission. Aalborg's merchants regarded every ambitious harbour on the fjord as a competitor to be strangled early, and they were extremely effective at it. Complaints from Aalborg produced a royal ban in 1598 on Løgstør's trade in grain and hardware. In 1752 the town's application for expanded trading rights was blocked again by the same interests. Fires ravaged the place in 1747 and in 1751, and by 1769 there were 392 people living here. Løgstør did not receive full market-town privileges until 1900 — nearly four centuries after it was first written down.

Agriculture, not fish, eventually made the town. Trade in farm produce needed infrastructure, so the harbour was enlarged, roads were laid, and the railway arrived in 1893. Commercial rights followed seven years later. In 1942 the Aggersund bridge was thrown across the fjord, pulling the southern part of Han Herred into Løgstør's hinterland. The physical evidence of the good years is still standing: Løgstør Church, neo-Gothic in red brick, finished in 1893 with a tall tapering tower facing west; Hotel du Nord beside the harbour; and, close to the water, Løgstør Grunde Fyr, a lighthouse of 1908 with two wooden towers rising from a white brick building, widely counted among the strangest and most attractive in Denmark.

The old centre is a grid of narrow streets lined with the low houses that nineteenth-century fishermen and sailors built for themselves. One of them was bought by Danish smallholders in 1918 and given to the writer Johan Skjoldborg, the novelist and playwright who had spent his career putting the rural poor of north Jutland into literature; he lived there until his death in 1936 and is buried in the churchyard. Løgstør has produced others. Peder Horrebow, born here in 1679, became an astronomer distinguished enough that a crater on the Moon carries his name. Jørgen Christian Jensen, born in 1891, emigrated to Australia and won the Victoria Cross. Today the town has 3,929 inhabitants (2026) and calls itself Muslingeby — Mussel Town — which is honest branding for a place whose fortunes have always been decided by what was in the water and whether anyone could get a boat to it.