The River Westbourne is a small River Thames tributary in London, primarily sourced from Whitestone Pond, Hampstead Heath which, notwithstanding meanders, flows approximately southward to skirt east of Hyde Park's Serpentine lake after about 3.3 miles (5.3 km), to Sloane Square, Chelsea after about 1 mile (1.6 km), passes centrally under the south side of Royal Hospital Chelsea's Ranelagh Gardens after about 0.5 miles (0.8 km), then issues into the Inner London Tideway.