The Nidda is a right-bank tributary of the river Main in Hesse, Germany.

It springs from the Vogelsberg on the Taufstein mountain range near the town of Schotten. It flows through the Niddastausee dam, and then through the towns of Nidda, Niddatal, Karben, and Bad Vilbel. At Harheim it reaches the Frankfurt am Main city area, and, after 90 km, flows into the Main in Höchst.

In the 1920s and 1960s, the flow of the Nidda was regulated to reduce the risk of floods. The original numerous meanders turned into bayous, while the riverbed was straightened and made deeper. In 1993, the Nidda was partially restored to its natural state and a bicycle path was built along the river.

The following rivers are tributaries to the river Nidda (from source to mouth):

• Left: Michelbach, Läunsbach, Eichelbach, Hohensteinerbach, Laisbach, Wehrbach, Selzenbach, Nidder, Edelbach

• Right: Graswiesenbach, Hohlbach, Gierbach, Ulfa, Salzbach, Hollergraben, Horloff, Wetter, Rosbach, Geringsgraben, Erlenbach, Eschbach, Kalbach, Urselbach, Steinbach, Westerbach and Sulzbach.

• Nidda estuary „Wörthspitze“ with houseboats
• The area around the source of the Nidda
• Mouth of the tributary Nidder