The river is from a hot spring
so we must make it bubble and steam.
and use it as the basis for your particle object.
Place Steam bottom centre in the River.
Change the settings of the Steam particles as shown
Angle the particles upwards
Make them mostly transparent.
Narrow the angle of the cone
Change the initial properties of the particle as shown.
Change the lifetime properties as shown
Test your game to see the Steam rising from the River