The Zwalm or Zwalmbeek is a tributary of the Scheldt and one of the main watercourses in the Flemish Ardennes in the southern part of the Belgian province of East Flanders.

The highest point in this source area is at 150 meters above TAW (Tweede Algemene Waterpassing).

The non-navigable Zwalm, along with the Ronne and the Maarkebeek, is the main tributary of the Scheldt River between Tournai and Ghent.

In the Middle Ages, in 976, the monks of St. Bavo's Abbey in Ghent founded a settlement at 'Ten Berge,' northeast of the confluence of the Wijlegemse stream into the Zwalm.

The following 11 species were caught in the Zwalm: perch, roach, three-spined stickleback, gudgeon, carp, chub (reintroduced in 2000), eel, rudd, European bitterling, pike, and tench.

The most fish-rich zone, both in terms of quantity and diversity of species, remains the downstream area with the Zwalm Mill pool.

The species found at that time, in order of abundance, were roach, European bitterling, spirlin, eel, three-spined stickleback, perch, gudgeon, carp, chub, blue bream, bream, river lamprey, European weatherfish, common bleak, smelt, rudd, tench, common minnow, Eurasian ruffe, vimba bream, sunbleak (reintroduced in 2015), and American brook lamprey.

[7][8] European bullhead is also found in the Zwalm basin (including in the Sassegembeek, Traveinsbeek, and Maarkebeek).

In the Zwalm region, much like in the rest of the Flemish Ardennes, day tourism is a predominant activity.

Along this path, completely free of car traffic, you can follow the Zwalm valley from Opbrakel to Zottegem.

You can also follow the Zwalmbeek from Opbrakel to its confluence with the Scheldt in Nederzwalm via a footpath starting from Moriaan and Jan de Lichtepad in Velzeke.

The lower course of the Zwalm and its dammed sections are navigable by small rowing boats and canoes.