premise: Three Mills Residential Moorings is a community of twenty residential narrowboats moored on the Three Mills Wall River Weir near Three Mills in the East End of London. Historically a tidal stretch of water, the residential moorings were converted to non-tidal in preparation for the London 2012 Olympics by the construction of a weir
hypothesis: The narrowboats continued to dock there during construction. 
reason: It wasn't told that the boats were moved or not. 