If you find yourself crossing one of London's busy bridges and look down, you may notice that the height of the Thames changes over the course of the day. When the tide (潮水) is out, you may see people move down hidden stairs to walk slowly along the foreshore (前滩). These are "mudlarks" — and they play a key role in preserving the history of the Thames by picking up objects and artefacts (手工艺品) hidden in the river's mud (泥).

Walking along the foreshore of the Thames is not everyone's idea of a hobby — it can be cold and dirty. When the tide turns, it turns fast. You must always be aware of your way off of the foreshore. The mud is anotherhazard. A more experienced mudlark said he had once fallen into the mud. He was lucky to have a bucket to move out the mud.

Historically, being a mudlark was a low station in life. The term came about in the 18th and 19th centuries when the Thames was one of the major ways to transport goods into the city. At this time, the banks of the river would be full of mudlarks, mostly poor women and children. As the tide dropped, they would walk into the mud to pick up lumps of coal, pieces of rope or anything else careless boatmen had dropped overboard that they could sell.

Mudlarking is experiencing a renaissance (复兴). It has never been easier for people to explore the Thames: anyone looking for inspiration just has to follow the mudlarking posts on the Internet. The Thames Discovery Programme, a group of historians and volunteers, run guided tours of the foreshore where experts guide you and ensure that you stay safe and stick to Port of London Authority rules.