sentences:  In 1829, the source of water was moved further up river to Lea Bridge as a result of pollution caused by population growth.In 1770, the Hackney Cut, had been built across Hackney Marshes to avoid a meander of the natural river course; clean water was now abstracted from the natural channel to a new reservoir at Old Ford.In 1830 the company gained a lease on the existing reservoir at Clapton.