The Transportation Safety Board of Canada has issued an investigation report (A17C0146) into this crash. It states in part that:
During the descent, the aircraft encountered icing conditions and the anti-icing and de-icing systems were activated. When the de-icing and anti-icing systems were turned off, residual ice remained on portions of the aircraft.
The aircraft stayed at the Fond-du-Lac Airport to board new passengers and cargo.
The operator, West Wind Aviation, had some de-icing equipment in the terminal building (see photos) at the airport. The de-icing equipment that was available to WestWind Aviation in Fond-du-Lac consisted of two ladders, a hand-held spray bottle with electric blanket and wand, and a container of de-icing fluid. However, the aircraft was not de-iced before takeoff, and the takeoff was commenced with ice contamination on the aircraft.
The Report can be found at
Aviation Investigation A17C0146 - Transportation Safety Board