Collet says that the water molecules form hydrogen bonds with the amino acids. As long as the temperature remains relatively high, the hydrogen bonds are constantly being broken and forming again and the folding proceeds in the usually rapid fashion.
But if the temperature drops, the hydrogen bonds become permanent, allowing the protein to take on new low-energy configurations. This dramatically changes the energy landscape, creating additional valleys that correspond to these new low-energy shapes. So instead of falling through the energy funnel, the protein becomes stuck in another valley that corresponds to an incorrect shape.