It will depend on your regional byelaws.
In Northumbria, there are such locations where it is illegal to fish from a specified distance downstream of the obstruction for any species any of the time; some where it is illegal to fish only at certain times of the year, notably September; and others where it is legal to fish immediately below the obstruction at all times of the season. Rivers with big runs of salmon & sea trout are more likely to have had these orders put in place.
Such restrictions are clearly defined in the EA byelaws for the Northumbria region, so I guess it will be similarly the case for others, but I could be wrong...
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