Covering Up The Zenne – Brussels’ Polluted Subterranean River

There are many instances throughout history of cities covering an urban river or stream, due to its size or non-use as a navigable waterway. Today we will look at one that was covered up 150 years ago in Belgium to hide pollution and waste water. Proper waste water treatment plants would not exist until 2007.


Around 1800, Brussels was in many ways still a very medieval city. The royal quarter in the upper town, inhabited mainly by the nobility and the richer members of the bourgeoisie, was upscale and modern. The rest of the city, however, in particular the lower town, located in the western half of the Pentagon, was densely populated and industrial, characterized by an illogical street layout, back alleys, narrow streets, and numerous dead ends.

The Zenne (or Senne) river split into two branches at Anderlecht, penetrating the Pentagon, the former site of the second city walls, in two places. The main and more southern arm entered through the Greater Sluice Gate, near today’s Brussels-South railway station. The smaller northerly arm entered through the Lesser Sluice Gate, near today’s Ninove Gate. The courses of the two traced a meandering path through the city centre, forming several islands, the largest of which was known as Saint Gaugericus Island. The two branches met up on the north side of Saint Gaugericus Island, exiting the Pentagon one block east of Antwerp Gate. A man-made arm, called the “Lesser Senne” (Frenchpetite SenneDutchkleine Zenne) continued on the borders of the Pentagon in the former moat, outside the sluice gates. It followed the Charleroi Canal before rejoining the main part of the Senne north of the city.

The Zenne in 1837 – Showing its man-made add ons and strangely winding 1-mile course through the city. During dry weather, the river became an open sewer, had a feeble flow- increasing issues like waste and bacteria, foul odor, due to lack of proper drainage.

The Senne had long since lost its usefulness as a navigable waterway, being replaced by canals, including the Charleroi Canal. The Senne had always been a river with an inconsistent flow, often overflowing its banks. In times of heavy rainfall, even the sluice gates were unable to regulate the flow of the river which was often swollen by numerous creeks flowing down from higher ground. Making matters worse, within the city the river’s bed was narrowed by encroaching construction due to demographic pressure. The supports of numerous unregulated bridges impeded water flow and caused water levels to rise even further, exacerbated by a riverbed of accumulated waste.

Above: Many unsanitary and unsafe wooden add-ons projected over the river in the lower town.

During dry periods, however, much of the Senne’s water was diverted for the needs of the populace of the city as well as to maintain the water level in the Charleroi Canal. This left a flow too feeble to evacuate the filthy water, leaving the sewage, garbage, detritus and industrial waste that had been dumped into the river to accumulate in the stagnant water. The Senne, which a witness in 1853 described as “the most nauseous little river in the world” had become an open-air sewer spreading pestilential odours throughout the city. Early in the second half of the 19th century, Brussels saw numerous dry periods, floods and a cholera epidemic, caused as much by the river itself as by the poverty and the lack of hygiene and potable water in the lower city. This forced the governments of the Province of Brabant and the City of Brussels to act.

Construction. Covering the Zenne in 1867.

Modern Brussels. One can still catch a glimpse of the Zenne. Here, it flows under the archways of this building.

The Zenne is seen here from a hidden alleyway near a remote courtyard.