A "dalyan", in English weir, in my own language (Dutch) "weer": a certain type of fish trap.
From the Wikipedia: A fishing weir, fish weir, fishgarth or kiddle is an obstruction placed in tidal waters, or wholly or partially across a river, to direct the passage of fish. A weir may be used to trap fish such as salmon as they attempt to swim upstream, or eels as they migrate downstream. Alternatively, fish weirs can be used to channel fish to a particular location, such as to a fish ladder. Weirs were traditionally built from wood or stones. The use of fishing weirs as fish traps dates back prior to the emergence of modern humans, and have since been used by many societies across the world.