Pielinen is the fourth largest lake of Finland, with a drainage basin area of 12,823 km (4,951 sq mi) that is equally distributed between eastern Finland and Russia. The creation of the lake and its outlet is attributed to a post-glacial isostatic rebound, which resulted in uplift of the land. As is common in Finnish lakes, the water color of the lake is dark on account of the high proportion of bogs present in the catchment of the drainage basin that drains humic substances.