Naknek Lake is a lake in southern Alaska, near the base of the Alaska Peninsula. Located in Katmai National Park and Preserve, the lake is 40 miles (64 km) long and three to eight miles wide, the largest lake in the park. The lake drains west into Bristol Bay through the Naknek River. The elevation of the lake has lowered over the past 5,000 years as it has cut through a glacial moraine, separating Naknek Lake and Brooks Lake and creating Brooks Falls about 3500 years ago.