Huai or Hwai (both: hwī), river, c.680 mi (1,090 km) long, rising in the Tongbai Mts., Henan prov., E China, and flowing E across Anhui prov., through Hongze Lake, to the East China Sea. The Huai marks the boundary between the N China Plain and the Chang delta. More than two thirds of the fertile Huai basin is under cultivation; wheat, millet, and kaolin are the main crops. An irrigation canal branches from the river to the sea. Receiving many tributaries, the Huai floods more frequently and over a larger area than any river in N China; since 1950 extensive flood control facilities, including eight dams, have been built.