WBs are a historic and longstanding way of policing rivers. A very brief outline here:
http://en.wikipedia.org/wiki/Water_bailiff
However, despite their police-like powers, there is little control of these guys or how they act and an appointment is often made from staff of the landowner/riparian owner, so they are very often rather determined in acting for those interests.
Recently things seem to be changing South of the Border, with WBs being directly engaged by the Environment Agency in England and In Scotland, by the various associations that administer river "Protection Orders" (which are very often not, but that's another thread), which again are often little more than a monopoly of vested interests lording it over everyone else.
Larger estates/riparian owners can still employ their own WBs and the vaugeries of the current legislation means that once appointed, they can operate on
any waters in the entire catchment area regardless of them being wanted there or not. There has been a longstanding feud between WBs for the estate near me and the public waters downstream, which has led to stand-up fights and a farcical court hearing, on the riverbank where the WBs were eventually found well and truly guilty of harrassment but still got wrist-slap fines and kept their jobs/WB appointments!