In the pre-Christian Sámi era places in the nature were believed to be sacred and connected to different gods or the spirit world. The sacred places often had a sacred place name and several of the sacred place names are still here today. One of the sacred places were sáiva-lakes which were believed to be sacred lakes that had two lakebeds, where the second or lower lakebed were considered connected to the spirit world. Sáiva-lakes were considered to be great fishing lakes but there were some rules that the fisherman had to obey to such as there had to be complete silence while fishing otherwise the fish would disappear down to the second lakebed. The sáiva-lakes were also connected to sacrificial practises, there were both sacrifices to the lakes or to sieidi stones on the lake shore for fishing luck or as a thank you for the fishes received. There were also sometimes bigger sacrificial places with different animal bones, sieidi stones and sometimes metal objects.Little is known or written about sáiva-lakes and most descriptions of sáiva-lakes comes from historic sources. The aim of this thesis is to research and contribute to more knowledge about sáiva-lakes and sacred traditions by lakes and watercourses in Northern Scandinavia. The main focus is to study sáiva-lakes both from a sacred and a nature perspective as well as to analyse how sáiva-lakes relate to archaeological sites and other sacred places and place names in their surroundings.The theoretic perspective applied on the thesis is mainly new animism and phenomenology which is applied to give a perspective on the landscape and nature. The study is based on archaeological material, historic sources, field excavations done by the author and a GIS analysis. The study shows that sáiva-lakes were connected to sacrificial practises and that sáiva-lakes often have other sacred places and places names in areas around the lakes. In a larger perspective the study of sáiva-lakes shows the perspective of a cultural landscape, and the aspect of sacred traditions by lakes and watercourses.