The Westbourne or Kilburn is a mainly re-diverted small River Thames tributary in London, primarily sourced from Whitestone Pond, Hampstead Heath and which, notwithstanding one main meander, flows southward through Kilburn and the Bayswater (west end of Paddington) to skirt underneath the east of Hyde Park's Serpentine lake then through central Chelsea under Sloane Square and it passes centrally under the south side of Royal Hospital Chelsea's Ranelagh Gardens before historically discharging into the Inner London Tideway. Since the latter 19th century its narrow basin has been further narrowed by corollary surface water drains and its main flow has been replaced with a combined sewer beneath its route.