With the evidence of few salmon returning to the Fraser River in the years following the 1914 rock slide at Hell's Gate, efforts were made by the governments of Canada and USA as well as the fishing industry, to form a partnership to rectify the passage problem in the Fraser Canyon and specifically at Hell's Gate.
No progress was made until 1937 when a joint Canada/USA Fisheries Commission was formed. This commission, named International Pacific Salmon Fisheries Commission (IPSFC), initiated immediate biological and engineering investigations for the purpose of solving the passage problem and rehabilitating the once historic salmon runs. By an engineering/hydraulic perspective and on the advice of the Commission’s engineering consultants, Professor C.W. Harris, Ted Pretious, P.Eng. & Dr. Henry Gunning, it was decided to leave the river margins as they were and build fishway structures to assist the salmon through the rapids at the known block stages. Consequently, the scheme devised by the engineers was to aid the natural river with fishways to perform its function without destroying the natural hydraulics.

Using topographic and hydraulic survey data from Hell's Gate carried out by the Board of Engineers Enquiry, 1926-1928 combined with additional field data obtained by IPSFC engineers, the Commission built an undistorted 1:50 scale model of the river (in concrete) at the University of Washington in Seattle in 1942. Extensive model tests showed conclusively that streambed clearing of slide material or excavation from either riverbank at Hell's Gate would be unwise. Furthermore the tests indicated that removal of rock from the bottom or sides of the river would result in unpredictable hydraulics as the flow changed, conditions which would be difficult to manage if obstruction to fish migration was to be solved. Jim Pyper, a Commission engineer carried out the model studies, and the results were instrumental in evolving the novel vertical slot fishways designed and built for the first time at Hell’s Gate.