The Yorkshire Water Authority was created in 1973 when several bodies related to drinking water supply, water resource management, drainage, sewage treatment and disposal were brought together. With privatisation in 1989 it went to the NRA and then the EA. What it was before 1973 i don't know.
As far as I can tell it was something like this Environment Agency1989: National Rivers Authority1973: Yorkshire Water Authority(renamed to Yorkshire River Authority some time between these dates)1965: Yorkshire Ouse and Hull River Authority 1950: Yorkshire Ouse River Board1930: Yorkshire Ouse Catchment BoardSo Rivers House will have been commissioned by the YOCB. After searching various archives including Wikipedia, Hansard and the Statute Law database I found something on Google Books called "Water management in the English landscape: field, marsh and meadow" by Hadrian F. Cook, Tom Williamson at http://books.google.com/books?id=ydXFAm75n0IC. My interest in this only goes so far but it's there if people want to have a look.