Admittedly, the pun in the title only works if you are familiar with South Yorkshire dialect. However, the industrial North has a particularly large selection of barriers to fish movement in the form of artificially engineered weirs. These affect all gravel spawning species of fish (from barbel, grayling and trout throught to the big hitters of the migratory reproducers; the eels and salmon). In addition, all barriers to movement (including weirs) reduce the ability of fish to avoid pollution incidents and/or subsequently return to their home patch. Moreover, the impoundment of water behind weirs increases the siltation by reducing current speed (sometimes for surprisingly long distances upstream of the structure - depending on weir head height and stream bed slope). Increased siltation is obviously not good for spawning gravels. Regulated slow flows also tend to homogenise the habitat in the impounded reaches, resulting in lower variety of invertebrates and fewer good holding features for fish. The fish that are present in the slower water are often very difficult to approach without spooking them in the flat water. However, it is almost universally true that the pool downstream of the weir (where the water rushes in providing oxygen, cover and more variable/interesting habitat) will be an excellent fish holding area. Therefore, in removing such barriers, you are often asking anglers to take a great leap of faith that the resultant overall improvement will be worth it. To those people, I would ask if I could take you fishing in pocket water this summer and lets see what we catch relative to our results in the canal-like sections.
The report I'm reading at the moment details plans to tackle the 24 weirs on the 8km of the River Sheaf (a tributary of the S. Yorks Don). The tributaries of the Sheaf itself house a further 20 weirs of their own. I read somewhere that the main river Don used to have something like 300 plus weirs - but that these days there are somewhere around 30 weirs on the main river that represent a "significant barrier" to fish movement.
P.S. the title translation would be "Where have you been?" rather than an enquiry as to the location of a waste receptacle.