The Lemhi River, a tributary of the upper Salmon River in Idaho, is managed as an Intensively Monitored Watershed (IMW). While 93% of the watershed is federally managed, the majority of the valley floor along the mainstem Lemhi is privately owned. At the inception of ISEMP, over 322 know irrigation diversions were operated to support agriculture, resulting in the dewatering of 28 of the 31 major tributaries to the mainstem Lemhi River. Moreover, the lower 48 kilometers of the mainstem Lemhi River have been simplified by road construction and agriculture. Local managers believed that loss of access to historically important tributary habitat and mainstem habitat simplification reduced the freshwater productivity of spring/summer Chinook salmon and steelhead in the basin.
The Lemhi Intensively Monitored Watershed monitoring strategy focuses on collecting fish and habitat data to inform a species-specific life cycle model. The model can then be used to predict the effects of restoration scenarios on fish populations.
- 2013: Project initiated
Findings and Uses
To date, tributary reconnection actions have almost doubled the length of stream available to anadromous salmonids, increased available stream area by 22%, and resulted a 19% increase in pool area.
Adult escapement, juvenile rearing, and increased densities of juveniles have been documented in restored habitat. Steelhead spawning has been documented in all reconnected tributaries; however, an increase in spring/summer Chinook or steelhead has not yet been detected, although it is predicted.
ISEMP’s development of quantitative fish-habitat relationships has improved our ability to identify life-stage-specific limiting factors and target habitat restoration actions to address them. Monitoring of site-based actions has increased our understanding of time-lags between project implementation and biological response. Most importantly, Lemhi IMW lessons are transferable to other watersheds in the interior Columbia River Basin, enabling more effective restoration elsewhere.
|Conservation Measure||Title||Geographic Area||Objective||Description|
|CM-01||Lemhi River Tributary Reconnects||Lemhi River Tributaries||Fish passage||Provide hydraulic and ecological connectivity between the Lemhi|
|CM-02||Removal of Irrigation Structures and Road Culverts that Inhibit Fish Passage||Basinwide||Fish passage||Identify fish passage problems and improve fish passage throughout the Lemhi River basin|
|CM-03||Fish Screening to Reduce Entrainment in Irrigation Canals||Basinwide||Fish passage||Screen irrigation ditches to reduce entrainment and associated mortality of fish in tributaries|
|CM-04||Eliminate Ditch Return Threats||Basinwide||Fish passage||Prevent fish from entering irrigation ditches from the downstream end|
|CM-05||Riparian Grazing Management||Basinwide||Riparian habitat protection||Improve riparian zones along the Lemhi River and tributaries to rehabilitate fish habitat|
|CM-06||Enhance Side Channels and Secondary Rearing Channels||Middle Reach|
|Stream habitat improvement||Provide fish access to side channels to enhance spawning habitats and juvenile rearing capacity|
|CM-07||Lemhi River Stream Channel Rehabilitation||Lower Reach|
|Stream habitat improvement||Restore large segments of the Lemhi River to improve habitat condition for spawning and rearing|
|CM-08||Pool Development||Lower Reach|
Stream habitat improvement
|Improve fish passage and rearing in the Lemhi River by increasing the number of pools|
|CM-09||Maintain Biologically Sufficient Conditions for Fish Passage in the Lower Lemhi River||Lower Reach||Fish passage||Minimum continuous stream flows below the L6 diversion and modifications to the river channel would be used to maintain biologically adequate fish passage for access to the middle and upper river reaches and tributaries|
|CM-10||Upper Lemhi River Chinook Salmon Assessment||Upper Reach||Stream habitat improvement||McFarland stream flow and fish performance study|
|CM-11||High Volume Flow to Improve Instream Habitat Conditions||Upper Reach||Stream habitat improvement||Provide high volume stream flows to maintain stream channel complexity and rehabilitate fish habitat|
|CM-12||Maintain Fish Passage in the Lower Reaches of Hayden Creek||Hayden Creek||Fish passage||Preserve continuous flows that historically have been available in lower Hayden Creek for migrating fish|