The covering of the Senne was one of the defining events in the history of Brussels. The Senne was historically the main waterway of Brussels, though it became more polluted and less navigable as the city grew. By the second half of the 19th century, it had become a serious health hazard and was filled with pollution, garbage and decaying organic matter. It flooded frequently, inundating the lower town and the working class neighbourhoods which surrounded it.
Numerous proposals were made to remedy this problem, and in 1865, the mayor of Brussels, Jules Anspach, selected a design by architect Leon Suys to cover over the river and build a series of grand boulevards and public buildings. The project faced fierce opposition and controversy, mostly due to cost and the expropriation and demolition of working class neighbourhoods. The construction was contracted to a British company, but control was returned to the government following an embezzlement scandal; this delayed the project, but it was still completed in 1871. The project's completion allowed urban renewal and the construction of the modern buildings and the boulevards which are central to downtown Brussels today.
In the 1930s, plans were made to cover the Senne along its entire course within the greater Brussels area, which had grown significantly since the covering of the 19th century. The course of the Senne was changed to the downtown's peripheral boulevards. In 1976, the disused tunnels were converted into the north-south axis of Brussels' underground tram system, the premetro. Actual purification of the waste water from the Brussels-Capital Region was not completed until March of 2007, when two purification stations were built, thus finally cleaning the Senne after centuries of problems.