Watts are the areas by the sea that are twice under water and twice in the air every day due to high and low tides. So this change takes place approximately every six hours. At high tide, the mud flats become the seabed.
In Germany, you can find mudflats on the North Sea. There are also mudflats on the North Sea coasts of Denmark and the Netherlands. If you mean the Watt and the areas around it, you speak of the Wadden Sea. Many plants and animals live in the Wadden Sea that only live here. Such creatures are called endemics. They have adapted well to the alternation of water and air.
The Wadden Sea is so important to nature that it is almost entirely a nature reserve. Plants and animals should be protected. That is why there are precise regulations as to what people are allowed to do there and what not.
When hiking on the mudflats, you go for a walk in the mudflats. You have to be careful not to get lost and get back to the mainland in time before the water comes back. Therefore, trips to the mudflats should only be made with someone who knows the area very well.