A fairly small bird of fast-flowing streams through foothill and montane forest or scrub. Slaty-blue with a rufous belly and tail. Female is a duller version of the male. Somewhat similar in color to Blue-headed Fantail, but has a shorter tail and is usually restricted to streams. Also similar to Blue Rock-Thrush, but smaller, with a dark tail. Song is a slightly ascending series of notes run together to sound like a quavering whistle.