One of the major rivers of Europe, the Elbe flows more than 1,000 kilometers (600 miles) across the continent before reaching the North Sea. At its mouth, the low-lying landscape is continually reshaped by the rise and fall of the tides. These dynamic tidal flats are a boon to biodiversity while sometimes posing challenges for those navigating its waters and for communities living along its shores.

The images above illustrate how the area changes with the tides. They were acquired on August 15, 2025, at low tide (left) and on May 11, 2025, at high tide (right) with the OLI (Operational Land Imager) on Landsat 9. The mean tidal range at Cuxhaven is 2.9 meters (9.5 feet), which is considered intermediate, or mesotidal. The tides are also asymmetrical, meaning the flood period is shorter than the ebb. This causes the incoming current to run faster and typically carry more sediment up the 140-kilometer-long (87-mile-long) estuary than it does out.

The low tide exposes complex channels, sandbars, and mudflats around the river mouth. This wide zone of coastal wetlands is part of the Wadden Sea, which stretches from the Netherlands to southern Denmark and represents the largest continuous system of intertidal sand and mud flats in the world. Its habitats serve as important staging, molting, and wintering grounds for migratory birds, with more than 10 million passing through every year.

A channel cuts through these natural features near the river’s mouth, allowing ships to reach Cuxhaven and Hamburg—the third-largest container port in the European Union—farther upriver. Dredging is required to remove accumulated sediment in the channel, and some ships can only pass through when the tide is high enough. The Elbe’s mouth also provides access to the Kiel Canal, which connects the North Sea and Baltic Sea and is the world’s busiest human-made waterway navigable by seagoing ships. 

At high tide (right), only a handful of small islands and sandbars remain above the waves. One of these islands, Neuwerk, is a tranquil tourist destination that is home to a few dozen inhabitants and the oldest building on the German coast. A brick tower, completed in 1310 and later converted to a lighthouse, was built to protect shipping on the Elbe from pirates and wreckers.

These images show normal tidal variation in the area, but storms can push water levels much higher than a typical high tide. The highest water level measured at Cuxhaven—5.1 meters (16.7 feet) above Europe’s official sea level reference—occurred on January 3, 1976, when a fast-moving storm swept across the North Sea and slammed the coast with high winds. Researchers who reconstructed historical storms noted that the storm surge was worsened by its timing relative to the tide. The strongest winds arrived around low tide, preventing water that had propagated upstream at high tide from flowing back out to sea and causing further inundation inland.

Scientists study past extreme events like this to better understand how future storms might affect low-lying coastal areas and how flood protection could be improved. Flooding risks can be exacerbated by rising sea levels, which at Cuxhaven have trended upward by 2.12 millimeters per year, or 0.70 feet per century.

Two new Earth-observing satellites are making it possible to measure water levels in coastal areas in greater detail. The dual-band radar on the NISAR (NASA-ISRO Synthetic Aperture Radar) satellite is expected to track long-term phenomena such as sea level changes, as well as to map flood inundation and other ephemeral events. In addition, early data from NASA’s SWOT (Surface Water and Ocean Topography) satellite has demonstrated the potential to accurately measure water levels around complex coastlines and to improve tidal models.

NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Photo by Thomas Gölles. Story by Lindsey Doermann.