Pit lakes develop in surface excavations at former mining sites. They can result from mining of sand, gravel, clay, lignite, hard coal, and metal ores, and in quarries. Synonymous terms used in the literature are “mining lake”, “mine lake,” and “mine pit lake”. The emphasis of this book is on pit lakes in former lignite, hard coal, and ore mines that are affected by acid mine drainage (AMD), and on respective management options to ensure acceptable water quality. Other pit waters without AMD inputs, such as fluvial gravel pit lakes, quarry ponds, and neutral or alkaline pit lakes, are not addressed, though the case studies in Chap. 5 of this volume include pit lakes in former sulfur mines and remediating the harmful effects of mining on nearby natural lakes.