Jefferson River - Ecology and Human Impact

Ecology and Human Impact

The Jefferson River consists of three distinct sections.

The upper Jefferson is a much-braided, meandering river and floodplain system that supports productive farm fields, extensive cottonwood groves, rich meadows, and abundant wildlife. The river creates diverse habitats as it naturally shifts back and forth across the Jefferson Valley, forming oxbows and swamps of various depth and age. Shifting channels and natural flooding facilitates the germination of cottonwood seedlings. Individual cottonwood groves are often germinated from a single flood event and tend to be of uniform age. The upper Jefferson extends from the confluence of the Big Hole and the Beaverhead rivers approximately 44 miles downstream to the community of Cardwell.

The middle Jefferson enters a narrow canyon a short distance downstream from Cardwell and is largely contained by the geography for most of the next 15 miles downstream to Sappington Bridge. Lacking the ability to flood or meander, this section of the river has few trees, swamps, meadows, and significantly less wildlife than the upper Jefferson.

The lower Jefferson opens up again into a meandering, braided river from Sappington bridge approximately 24 miles downstream to its confluence with the Madison River. Here, the riparian zone again supports an extensive community of swamps, meadows, cottonwood groves, and productive farm lands.

Throughout its length, the Jefferson River is used extensively as a source of irrigation water for local farms and ranches. Dams constructed upstream on the Ruby and Beaverhead rivers store surplus water from spring runoff which is released to augment natural flows during the summer irrigation season. However, portions of the river can become severely dewatered, shallow, and warm in drought years, adversely impacting fish populations. The unnaturally warm water, combined with excess nutrients from irrigation runoff and grazing practices, can stimulate rapid growth of algae in mid-summer, to the detriment of anglers and floaters.

While much of the Jefferson River remains untouched and scenic, it is threatened by new housing developments that incrementally fragment wildlife habitat and vistas along the river. Efforts to stabilize portions of the riverbank with rock, concrete, and other rip-rap materials have inhibited the river's ability to flood, meander, and form new cottonwood groves and wildlife habitat. In addition, rip-rapped sections of the river tend to funnel floodwaters downstream, increasing the impact to other landowners.