The lower 30 miles of the Umatilla River is heavily diverted for agricultural use.

Historically, inadequate flow and passage conditions in this section of river during critical portions of both adult and juvenile migration periods contributed to the extirpation of salmon and decline of summer

credit: Wikimedia Commons

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steelhead populations in the Umatilla River.

Passage improvements have been completed at all five of the major irrigation diversions in the lower 30 miles of the Umatilla.

Additionally, Reclamation constructed Phase I and II of the Umatilla Basin Project shown below to provide flow enhancement in order to ameliorate flow conditions in the lower river.

Phase I exchanges Columbia River water with West Extension Irrigation District (WEID) for instream lows historically diverted by WEID to provide passage flows below Three Mile Falls Diversion Dam.

Phase II:
The Umatilla Basin Project is divided into three components for the exchange of Columbia River water with:
(1) Hermiston Irrigation District (HID) for instream flows historically diverted by HID to provide passage flows below river mile 2 8. 5. (2) Stanfield Irrigation District (SID) for instream flows historically diverted by SID to provide passage flows below river mile 3 2. (3) SID for reservoir storage capacity in McKay Reservoir which can be released for fish passage during critical migration periods.