Water enters the lake from the Italian Garden at the north-western end of the Long Water, where the (now buried) River Westbourne feeds a set of four ornamental fountains, which in turn flow into the lake. The Long Water runs south-east from this point to Serpentine Bridge, where the lake curves sharply to the east. At the eastern end water flows out of the lake via a sluice in the dam, forming a small ornamental waterfall. Historically, the river flowed due south from this point marking the boundary between Westminster and Kensington; since 1850, the river has been diverted into a large pipe, running underground to join the Thames near Chelsea Bridge.
The lake is relatively shallow, with a maximum depth of 40 feet (12 m).
In 1730 Queen Caroline, wife of George II, ordered the damming of the River Westbourne in Hyde Park as part of a general redevelopment of Hyde Park and Kensington Gardens. At that time, the Westbourne formed eleven natural ponds in the park. During the 1730s, the lake filled to its current size and shape. The redevelopment was carried out by Royal Gardener Charles Bridgeman, who dammed the Westbourne to create the artificial lake, and also dug a large pond in the centre of Kensington Gardens (the Round Pond) to be a focal point for pathways in the park.
At the time of construction, artificial lakes were long and straight. The Serpentine was one of the earliest artificial lakes designed to appear natural, and was widely imitated in parks and gardens nationwide.
The lake achieved notoriety in December 1816 when Harriet Westbrook, the pregnant wife of the poet Percy Bysshe Shelley, was found drowned in the Serpentine having left a suicide note addressed to her father, sister and husband. Shelley married Mary Wollstonecraft Godwin less than two weeks later.
The lake formed a focal point for the 1814 celebrations commemorating the British victory at Trafalgar, and of the 1851 Great Exhibition, with The Crystal Palace standing on its southern shore. Following the introduction of more stringent regulations to protect the environment in the park, the relocation of the Crystal Palace, and the construction of the nearby Albertopolis complex of museums and exhibitions, large-scale events ceased to take place on the banks of the Serpentine. However, it was the location for the 1977 Silver Jubilee celebrations, and will serve as a venue for the 2012 Olympics.
In the 1820s, the park was extensively redesigned by Decimus Burton. At the same time, John Rennie built the Serpentine Bridge to carry the newly built West Carriage Drive along the boundary between Hyde Park and Kensington Gardens, formally dividing the lake into the Serpentine (east) and the Long Water (west).
The Long Water is surrounded by dense overgrowth for much of its length, and is relatively undeveloped in comparison to the Serpentine. Due to its undisturbed nature, it forms a significant wildlife habitat and is designated as a bird sanctuary. A 2005 survey showed it as home to 90 species of moth alone. On the western bank of the Long Water, deliberately hidden in foliage, is a bronze sculpture of Peter Pan by George Frampton. The "real world" elements of the play and novel were set in the park and in the surrounding streets.
The Serpentine will be used for the swimming leg of the triathlon at the London 2012 Olympics.
London's Holocaust Memorial is situated at the eastern end of the Serpentine, immediately beyond the dam, and a memorial on the northern shore of the lake commemorates the Norwegian Defence Forces' role in World War II.
The Diana, Princess of Wales Memorial Fountain is sited on the southern shore of the Serpentine near West Carriage Drive. It currently receives approximately one million visitors per year.
Ranger's Lodge, immediately to the north of the lake, was the former head office of the Royal Parks Constabulary. Following the RPC's abolition in 2004, it is now the headquarters of the Metropolitan Police Service's Royal Parks Operational Command Unit, although as with the rest of the MPS, command and control of day-to-day incidents has been centralised to the Metcall complex.
The Serpentine Gallery, one of London's leading art galleries, is not in fact located on the Serpentine, but in Kensington Gardens, on the western side of West Carriage Drive immediately south of the Long Water.
The Rose Gardens at the southeastern corner of the Serpentine have in recent years become a popular meeting place for London's gay community. It has been alleged that their popularity as a cottaging location is due to their proximity to Hyde Park Barracks.