Harle (gat)
For most of recorded history, the island of Wangerooge has been moving. Not by much - a few meters a year, sometimes more, sometimes less - but consistently east, on a slow current of erosion that gnawed at its western flank and dropped fresh sand on its eastern tip. The water doing the eroding has a name. It is the Harle, also called the Harle Seegatt, the tidal strait that runs north-to-south between Wangerooge and the island of Spiekeroog. For centuries it was the most patient bulldozer in the German Bight. In the 1960s, engineers built a wall to make it stop.
A Channel Between Islands
The Harle Seegatt threads its way through the gap between Spiekeroog to the west and Wangerooge to the east, draining the Wadden Sea behind them into the open North Sea on each falling tide. The main channel splits as it approaches the islands - one branch, the Alte Harle, runs through what is also called the Muschelbalje; the other, the Dove Harle, leads into the port of Wangerooge itself. Like every channel in this stretch of coast, its course and depth shift with the seasons. German maritime authorities publish revised soundings every month in the official Notice to Mariners. A skipper who has not checked the recent figures has no business in the gat at all.
The Walking Island
Wangerooge drifts. Of all the East Frisian Islands, it has historically moved farthest and fastest, and the Harle is the reason. The strait's currents eroded the western tip of the island with a steadiness that no village or pier could outlast. Old maps, laid one over another, show the western beach retreating by hundreds of meters across a single century. Houses and dunes that once stood at the edge of the village ended up under the waves. The villagers built and rebuilt, and the sea kept setting the boundary. The eastern tip of the island, meanwhile, kept growing as the same currents deposited the sand they had stripped from the other end - the island walking east, in effect, one tide at a time.
Concrete and Groynes
The walking stopped, mostly, in the 1960s. The Wilhelmshaven authorities built a concrete barrier along the western shore of Wangerooge and a system of groynes - long fingers of rock running out into the water - designed to break the current and trap sand. The longest groyne reaches almost from the western end of Wangerooge to just in front of the eastern tip of Spiekeroog. It cannot be crossed at high tide, even by shallow-draft boats, and it sits as a serious hazard for any vessel that tries to traverse the strait outside the marked channel. The engineering worked. Wangerooge no longer marches east. Whether this counts as a victory or a kind of imprisonment depends on whether you are reading the geography or the spreadsheet.
The Port's New Boundary
More recently, the expansion of the harbor area on Wangerooge has changed the line on the chart. Niedersachsen Ports - the regional ports authority - now manages the transition zone between the inner harbor and the open strait, in a channel known officially as the Wangeroog Ansteuerung, the Wangerooge Navigation. The Harle remains a North Sea tidal channel, restless and changeable, but a slightly tamer one than it used to be. Tour boats and ferries pass through carrying day-trippers to the island; charter fishing crews still grumble about the groyne. From the air, the whole arrangement looks like a series of pencil marks across the surface of a moving carpet - lines drawn over something that will not stop moving underneath.
From the Air
53.78N, 7.83E. The Harle is best seen at low tide from 2,000-4,000 ft, when the groynes and channel structure are visible. The gat lies inside the Lower Saxony Wadden Sea National Park; observe the seasonal no-fly buffers over bird-breeding areas on both islands. Wangerooge airfield (EDWG) is at the eastern end of Wangerooge; the nearest larger field is Bremerhaven (EDWB) about 50 km southeast. Visibility usually best in the early afternoon; fog common at dawn and dusk.