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This is a sporting complex is being used for the 2012 Summer Olympics and the 2012 Summer Paralympics, situated to the east of the city adjacent to the Stratford City development. It contains the athletes' Olympic Village and several of the sporting venues including the Olympic Stadium and Aquatics Centre. The park is overlooked by ArcelorMittal Orbit, an observation tower and Britain's largest piece of public art. After the Olympics, the park will be known as Queen Elizabeth Olympic Park, to commemorate the Diamond Jubilee of Elizabeth II.
See Link for more details on the various parts of the park.

The River Lea (or Lee) originates at Marsh Farm Leagrave, Luton in the Chiltern Hills and flows generally southeast, east, and then south to London where it meets the River Thames. The river is 42 miles long.
Wikipedia: Link