When building a fish pass, there are several different factors that need consideration, aside from the obvious requirement for fish passage! One of these is the impact that the creation of a fish pass may have on features of archaeological significance. We have encountered this issues in the past at some sites, including the fish pass we designed in the Derwent Valley Mills World Heritage Site.
A series of fish passes we have designed on the Sheffield Don for the Don Catchment Rivers Trust are currently under construction, starting with the large Steelbank weir. An archaeological watching brief is ongoing during the excavation into the weir and so far some interesting artifacts have been found, including two cannonballs! An update on the excavations so far can be found here: https://doncatchment.wordpress.com/2016/08/04/steelbank-excavations/