Twin Falls County Water Intelligence Brief

September 21, 2026 | Agricultural Edition

Situation Summary

Snake River flows at Milner Dam are reporting at 0 cfs as of September 21, consistent with late-season diversion drawdown, while the downstream gauge near Twin Falls is recording 517 cfs — reflecting return flows and tributary inputs below the main diversion point. For Twin Falls County irrigators, this signals that the Snake River at Milner is in its characteristic end-of-season managed condition, with delivery reliability now dependent on what remains in upstream American Falls and Palisades storage. Reservoir storage data and 7-day forecast details are available in the full brief.

Snowpack Conditions

All three SNOTEL stations in the region are reporting at their expected late-season baseline for mid-to-late September:

Lewis Lake Divide — the station Twin Falls County irrigators watch most closely, as it monitors snowpack above the upper Snake River headwaters feeding Jackson Lake and downstream reservoirs — shows 0.0" SWE. No percent-of-median is reported for this date, meaning the median SWE for September 20 is also 0.0". This station is at its normal seasonal condition for this point in the calendar.

The 2026 seasonal context: Lewis Lake Divide and regional stations melted out 4–6 weeks ahead of the historical median meltout date, driven by the anomalous March heat wave. That early meltout advanced peak Snake River runoff into spring and reduced the summer carry into American Falls and Palisades storage. That event is now background history — the current story is what flows and storage remain for the final weeks of the irrigation season.

Streamflow Conditions

Two USGS gauges bracket the Magic Valley diversion system:

The 0 cfs reading at Milner is the defining signal: Twin Falls Canal Company and Northside Canal Company together divert essentially the full Snake River flow at Milner Dam during the active irrigation season, and this gauge confirms that late-season diversion is capturing available flow at the headworks. The Snake River below Milner does not function as a free-flowing river during irrigation season — it is a managed diversion system, and 0 cfs at Milner reflects normal operational conditions at this stage of the season.

The 517 cfs recorded near Twin Falls reflects return flows, groundwater contributions, and tributary inputs entering the river below the Milner diversion point — not mainstem Snake River delivery capacity. Both readings are reported as stable.

Seasonal Guidance

Subscribe for the full brief including reservoir storage, weather forecasts, depletion analysis, and detailed operational recommendations.

Data Sources: SNOTEL data through September 20, 2026; USGS streamflow data through September 21, 2026.

Important Disclaimers: This brief provides automated analysis for informational purposes only. Specific numerical claims have not been independently verified. Consult official sources including Twin Falls Canal Company (primary south-bank diverter at Milner Dam), Northside Canal Company (north-bank diverter), Idaho Department of Water Resources — Water District 36 watermaster (middle Snake River priority administration), and U.S. Bureau of Reclamation, Pacific Northwest Region (Boise office) for American Falls Reservoir and Palisades Reservoir upstream storage context. For water rights administration and ESPA monitoring, contact IDWR Eastern Regional Office, Pocatello, (208) 525-7161.