The first pioneers walked to the Wadden Sea islands in the 1930s, finding the route through ever-changing sand banks in the muddy seabed, usually due to emergency, when low tide would have grounded all boats. Since 1968, Sea Walks Center Friesland (Wadlopen centrum Friesland) organizes professionally guided walks for anyone fit enough to try. Every weekend from June to early September, the sea bed between Frisian coast and Dutch islands is full with trekkers, walking over living shellfish, rushing across towards the nearest island to beat the high tide. "It's the only place in the world where you can walk on the bottom of the sea to one of the islands. It's very unique," Jaap (63), one of the most experienced guides, explained. There are only two extremely short stops for walkers on the three hour journey to the island of Ameland. Each stop is barely long enough to sip some water, since timing is crucial. Latecomers risk being cut-off by a rushing high tide only to be rescued by the coast guard, once the water gets deep enough for their boats to operate. "As a guide, I would have to know where to walk, I'd use sea charts to determine my route basically, and in addition I'd need to know when to walk to the islands, so I need timetables to determine when to go, because tides are shifting every day for an hour or so, slightly less, I cant go at the same time tomorrow to Ameland, so I need to calculate when to go," Kees, a Frisland Sea Walk Guide told Reuters Television. "It's flood now. That means that this water basin is filling again and these ditches might cut our way off from the island. Ditches would have been too deep for us to way through, we'd have to call the coastguard and they'd need to rescue us," he added. A unique body of water, the Wadden Sea, lays between the coastlines of Friesland, Germany and Denmark and the North Sea. It is typified by extensive tidal mud flats, deep tidal trenches and islands. The sea on the other side of these islands is a deep, cold North Sea. Sea-Walking or "Wadlopen" in Dutch, is a traditional practice in the north of Netherlands and Germany. Wadlopen is only allowed under the supervision of licensed guides, who will lead walkers onto the organized routes on which they are allowed to traverse the seabed. The 'Wadloopcentrum Friesland' in the coastal town of Holwerd is a center for the training of guides and the preservation of the sport. Certain "hardcore" routes through the seabed are known but not recommended, either because of their inherent danger, the minimization of ecological disturbance, or both. The Wadden Sea is famous for the rich fauna, avifauna and flora. A great part of the Wadden Sea is now protected in cooperation of the Netherlands, Germany and Denmark. ENDS.