Harnes (French pronunciation: [aʁn]) is a commune in the Pas-de-Calais department in the Hauts-de-France region of France.

[3] Harnes is an ex-coalmining and light industrial town situated some 4 miles (6.4 km) northeast of Lens, at the junction of the D162e and the D39.

In the old riverbed of the Deûle/Souchez river (long-since drained by the creation of the Lens canal) and on the former mining area, the local authorities have created a landscape whose objective is to supplement the wastewater treatment leaving the sewage treatment plant at Fouquières by biological methods to eliminate pathogens and phosphates.

Five successive treatments are employed, involving filtration by coppiced willow, tanks planted with reeds, iris, bulrush etc., oxygenation and exposure to sunlight.

This project, which took five years to build (1999–2004), was awarded the “Rosa Barba” at the fourth biennial European landscape congress in Barcelona.