Mackenzie River from the Peace-Athabasca system are significantly slowed by the delta area at the western end of Lake Athabasca causing the lake to rise, and the excess water can only flow out after the rivers have receded. The same phenomenon occurs at Great Slave Lake, which naturally regulates the flow from the Slave River into the Mackenzie. There are river gages at several upstream points along the Mackenzie River. The average flow rate at the outlet of Great Slave Lake is . At Fort Simpson, below the Liard River, it is . At Norman Wells it is , and at the
Churchill River (Hudson Bay) and the rest flows as the Churchill River into Hudson Bay at Churchill, Manitoba. (see also Nelson River Hydroelectric Project) The Churchill formed a major part of the "voyageur highway" in the 18th to 20th centuries after Dene people showed Peter Pond the Methye Portage which connects the Hudson Bay watershed with the Clearwater – Athabasca – MacKenzie rivers which flow to the Arctic Ocean. See Canadian Canoe Routes (early). The Churchill is also home of several fish species including: walleye, sauger, yellow perch, northern pike, lake trout, lake whitefish, cisco, white sucker, shorthead redhorse, longnose sucker, lake sturgeon and