Lake Atna (; also known as Lake Ahtna) was a prehistoric proglacial lake that initially formed approximately 58 ka (thousand years ago) in the Copper River Basin, an area roughly centered around northeast of modern-day Anchorage, Alaska. The lake formed and dispersed during the Wisconsin glaciation. The lake existed in several forms, with several prominent shorelines observable in modern geology. At its greatest extent, the lake surface area was approximately half the size of modern-day Lake Ontario, and possibly much larger. The basin of the lake lay within an area bordered by the Alaska Range to the north, the Wrangell Mountains to the east, the Chugach Mountains to the south, and the Talkeetna Mountains to the west. Lake Atna may have generated several of the largest ever glacial lake outburst floods. One such flood may have contributed to the destruction caused by the 1964 Alaska earthquake.