Shortly after the retreat of the glaciers, the majority of the park water bodies were isolated from the large rivers by an uplifting of the earth’s crust, creating natural barriers for the fish. This phenomenon explains why originally the Eastern Brook Trout was the only species found in most of the streams and lakes. The invasion of the Champlain Sea at this same period permitted the Arctic Char, Ninespine Stickleback and Spoonhead Sculpin to colonise the low altitude lakes that form the network of lac à la Pêche, Isaïe, Français and Berubé lakes.
Today, there are 20 new species of fish that have been voluntarily or involuntarily introduced by man. Generally, the most accessible water bodies are those that have received the most new species (18 in lac à la Pêche, 9 in Wapizagonke Lake and 8 in Édouard Lake). The introduction of these species has had a dramatic effect on the indigenous ones, particularly the Brook Trout. Without the presence of the Laurentian and Shawinigan Clubs, the situation would have undoubtedly been worse.