The Owyhee Reservoir near Adrian, Ore.

A March 13 flight over the Owyhee River Basin left irrigation manager Clancy Flynn cautiously optimistic about this season’s water supply.

The river runs from Nevada north into Idaho and Oregon, draining about 11,000 square miles.

“Generally, on the east side of the canyon, we still have good snowpack and most of the draws are still frozen,” said Flynn, general manager of the Nyssa, Ore.-based Owyhee Irrigation District. “On the west side, all the draws were running with muddy water. Everything was letting loose over there.”

Owyhee Reservoir near Adrian, Ore., can hold 1.12 million acre-feet of water, of which about 715,000 acre-feet is available for irrigation. In a single season, more than 500,000 acre-feet is needed to deliver a full allotment. The reservoir irrigates more than 120,000 acres in three districts.

Reservoir volume as of March 13, when Flynn viewed much of the basin in a small plane, was more than 40,000 acre-feet behind the year-earlier level. The gap continued to narrow as of March 15.

Snow-water equivalent in the basin was 144% of the 1991-2020 median as of March 15, the Natural Resources Conservation Service reported.

“There’s more than enough SWE out there to make up for any deficits compared to last year” and “a fair amount left to come off,” Flynn said.

If runoff arrives efficiently, “there is a good chance we will be at least as we were last year” in terms of supply, he said.

“It still has to come off right,” Flynn said. “You never know what’s going to happen.”

Ideally, runoff flows to the reservoir efficiently as temperatures increase and conditions stay warm, he said. Efficiency drops when warm days are followed by cold days and even colder nights as runoff freezes, thaws and soaks into the ground before flowing downhill.

Some runoff came early last year but then slowed. It jumped following substantial snow in April and heavy rain in May and early June.

The Owyhee district’s governing board a year ago set the allotment at 2.1 acre-feet but later increased it to 3.1 acre-feet — 77.5% of full allotment, which is 4 acre-feet. The district irrigates about 1,800 parcels.

A couple of in-district transfers were completed last year — a customer can leave one field fallow and transfer its share of water to another, for example — but that activity stopped when the allotment was increased, Flynn said.

The board was slated to start discussing this year’s allotment March 21.

The district also pumps water from the Snake River. That allotment did not change last year.