Tamarix ramosissima Ledeb.
Small tree or shrub, 5 to 20 ft tall.  Leaves are small and scale-like.  Flowers are pink to white with 4 or 5 petals depending on species.

An ornamental that has naturalized along streams, river and canals in the West. Large plants transpire 200 plus gallons of water per day; drying up ponds and streams.

Monoculture growth severely limits wildlife diversity.  Also known as tamarisk.
Photos and information adapted from "Weeds of the West" by Tom Whitson