The reservoir was created by flooding Cockman's farm in 1835. The Brent and the Silk brooks were dammed and the water from the lake was used to supply the Grand Union Canal.
At its greatest extent it covered 400 acres (c1853), but was reduced in the twentieth century to 110 acres. Even so, it is said to contain enough water to fill three million baths, and in 1991 was believed to contain 10,000 lb (4,500 kg) of fish.
The reservoir is popularly known as the Welsh Harp after an inn of the same name. Originally called The Harp and Horn (c1750s) it was run by William Perkins Warner and his brother Jack. They ran it as a centre for sporting events, such as ice skating, swimming, angling and, until 1878, the Kingsbury Race Course.
At its height in the 1880s the lake attracted 25,000 people on Bank Holidays. The resort even had its own station from 1870, but the station closed in 1903 after the lake become less popular.
The reservoir was an important centre for speedboat racing in the 1920s and 1930s. C Harrison broke the outboard motorboat record at 57 mph (92 km/h) in 1931. The Welsh Harp Inn was demolished in 1970 to make way for the M1.