 The South Branch, which begins near Tavistock and initially flows southeasterly before turning southwesterly towards Woodstock, is the main stem Thames River and officially carries the Thames River name.The Thames River and North Thames River in the upper part of the watershed flow through valleys created during the retreat of the glaciers during the last ice age.The Thames River and North Thames River meet in central London at the "Forks"; the University of Western Ontario is located north of the Forks at the north branch's confluence with Medway Creek.