The size of river plumes in the Arctic Ocean is influenced by tidal mixing in estuaries. The Yenisei and Khatanga rivers have similar plume sizes despite different discharge rates. The Khatanga plume is large and diluted due to strong tidal mixing, while the Yenisei plume is smaller and more concentrated because of low tidal velocities. Tidal mixing affects the freshwater fraction in river plumes, determining their depth and area in the coastal sea. This means that the size of a river plume can be influenced by estuarine tidal mixing as much as by the river's discharge rate and wind.