There is a huge difference between high and low water levels around Hallig Oland. At high tide, ships can easily sail to the harbour. But at low tide, they are stuck in the mud. And at low tide you can take the Lore train to the mainland, or even walk to a nearby island across the seabed!
So what causes tides? It is all to do with the planets - The moon has a strange 'pull' effect on the oceans. So as the moon circles the earth, the oceans water levels go up and down. The sun also has an effect: together with the moon it can cause very high tides. If there are bad storms at the same time, you can get severe floods.
Many people on Hallig Oland work in coastal defence because these small islands are always in danger from wind and water, especially with the threat of global warming.
