The Branch River is a major tributary of the Wairau, with its headwaters in the Raglan Range. The Branch has a median flow of 14.8 cumecs, however capable of producing peak flow of 1800 cumecs.
The river is rich in biodiversity, with the following species having been observed; brown trout, rainbow trout, dwarf galaxias, koaro, upland bully, northern flathead galaxia, alpine galaxias, longfin eel, shortfin eel and kōura (freshwater crayfish).
Numerous aquatic invertebrates are also present.
(source: NIWA Environmental Monitoring and Observations (NEMO) database)
A hydro-electric scheme that diverts water from the river into a storage lake and canals is the largest source of electricity generation in Marlborough. The power scheme was first considered in 1978 but was not built until 1984. The construction involved sizeable earth works as a large artificial lake had to be built into which the river is diverted. The lake, Lake Argyle is well stocked with trout and is popular with picnickers and fishermen alike. The entire scheme operates automatically and produces 11MW of power for Marlborough. The hydro scheme was formerly owned by the Marlborough Electric Power Board, but after electricity reforms by the National government, the hydro scheme was sold to Trustpower.
Parts of the lower catchment include a former New Zealand Forest Service forestry trial in which a number of exotic species were been planted. Much of this area is now used for exotic plantation forestry. Beyond the plantation forestry, much of the catchment forms part of the Leatham Conservation Area, with vegetation ranging from manuka and kanuka scrub to beech forest, and alpine herb fields at higher altitudes. Wilding conifers are a significant problem in the conservation area.
Several huts a located near the river or its tributaries, and a four wheel drive track follows the river as far as Griegs Hut. The area is popular with hunters as pigs, deer and goats are found in reasonable numbers.