Separating Stockholm City Centre from South Stockholm, or, more locally, Norra Hammarbyhamnen on eastern Södermalm from Södra Hammarbyhamnen [sv], it connects Saltsjön to Årstasjön.
Originally a lake about 3 metres deep, it was transformed into a canal when connected to Saltsjön in the 1920s and a 6 metres deep channel was dug between Hammarbyslussen [sv] and Saltsjön and another to Sickla sluss [sv].
The importance of the water expanse has grown since the late 20th century as new residential areas have been constructed along its shores.
[1] Four bridges stretch over Hammarby Sjö and connected bodies of water: Danviksbron, Skansbron, Skanstullsbron and Johanneshovsbron.
Media related to Hammarby sjö at Wikimedia Commons