Putting back the Pahsimeroi, piece-by-piece
By Matt Green
In September 2016, Trout Unlimited partnered with the Bureau of Land Management, Bureau of Reclamation, and Idaho Department of Fish and Game to rehabilitate 0.8 miles of the mainstem Pahsimeroi River to improve salmon and steelhead habitat. Over a century of irrigation, which dewatered the streams for much of the year, has left the upper Pahsimeroi and its tributaries just stringers of dying cottonwoods running across a broad sagebrush valley.
After a few big spring freshets and several TU fish projects, including reconnecting tributaries to the mainstem and promoting irrigation efficiencies, those cottonwood strings are filling up with young seedling recruits as water has flowed through these reaches for longer each year. Without water in the streams, the trees slowly die and are no longer recruited to the river. This leaves the channel devoid of large and small debris and therefore very little complex fish habitat.
That’s where we decided to start—creating fish habitat. We installed approximately 100 pieces of large wood over the nearly one-mile stretch of river to jumpstart natural stream processes: scouring pools, pushing water into side channels, sorting gravels and silt to create spawning habitat and point bars where plants can establish, and slowly aggrading the channel and raising the water table.
Along with installing the large wood, we planted several hundred potted plants along the banks and floodplains. With Chinook salmon and steelhead just downstream of this reach, we’re hoping that fish will pioneer into these waters as they improve with more flows and better habitat. In fall 2017, we will work on another 1.3 miles of river just downstream of this reach to connect really great fish habitat further downstream.
Matt Green is Upper Salmon Project Manager for Idaho Trout Unlimited.