The next two months or so will determine whether the water of Phillips Reservoir climbs farther up the shoreline than it has in almost a decade.

Predicting the reservoir’s rise, though, is a task fraught with uncertainty.

“I don’t even have a clue what’s going to happen,” Jeff Colton, manager of the Baker Valley Irrigation District and the man who controls water releases from the reservoir, said on Tuesday morning, April 8.

Colton said the water supply outlook is considerably better, though, than it was during the drought that dominated from around 2018 through 2022.

During those years the reservoir along the Powder River, in Sumpter Valley about 17 miles southwest of Baker City, never came close to reaching 73,000 acre-feet, which Colton said is considered full.

(The reservoir can store an additional 17,000 acre-feet if needed for flood control. One acre-foot of water would cover one acre of flat ground to a depth of one foot. One acre-foot equals almost 326,000 gallons.)

That meant less irrigation water for many farmers, primarily in the Baker Valley. Water from the reservoir, which was created in 1968 by the construction of Mason Dam, irrigates more than 30,000 acres.

On Tuesday morning the reservoir was holding slightly more than 40,000 acre-feet — 55% of full.

By late summer each year from 2018-22, after the irrigation season, the reservoir dropped below one-quarter of its capacity.

And the subsequent winter snowpack, the main source of water to replenish the reservoir, wasn’t sufficient to refill such a severely depleted body of water.

The drought began to ease in early 2023.

The reservoir was nearly empty, with a little more than 5,000 acre-feet of water, at the start of April 2023.

But the combination of an above-average snowpack in the upper Powder River basin, and a stretch of warm weather in early May that rapidly melted the snow, pushed a glut of water into the reservoir that continued for weeks.

From early April to early June 2023, the reservoir rose by about 46,000 acre-feet. It peaked, on June 16, 2023, at 53,600 acre-feet, the most since early August 2017.

(2017 was also the last time the reservoir filled.)

The next spring, 2024, was quite different.

The reservoir held much more water than a year earlier — about 42,000 acre-feet in early April, compared with 5,000 the previous year.

But the snowpack wasn’t as deep — about 40% less than in 2023 — and the runoff was comparatively scant.

The reservoir added just 11,000 acre-feet during April and May.

Its peak, reached in mid-May rather than mid-June, was almost exactly the same, at 53,400 acre-feet.

The current snowpack occupies a middle ground between the previous two years.

As of April 8, the water content in the snow at an automated station near Bourne was 17.8 inches. That’s more than the 12.8 inches on that date in 2024, but less than the 21.3 inches on the date in 2023.

The problem, Colton said, is that the snowpack, although a useful barometer for estimating runoff into the reservoir, is hardly a definitive one.

The amount of water that flows into Phillips can vary dramatically from one year to another, even when the snowpacks are similar, he said.

Other factors that are more difficult to measure, such as how much of the melting snow soaks into the ground rather than flowing directly into streams, can have a major effect on the reservoir level, Colton said.

Another vital matter is when downstream farmers with rights to water stored in the reservoir start to ask for the water — and how much they need.

During a warm, dry spring, the demand for irrigation water can swell as early as April.

But if the season is cool and damp, Colton might be able to store most of the water flowing into the reservoir, holding it until the heat of summer.

The complications continue, though.

The same weather pattern that delays irrigation and keeps water in the reservoir also stifles the rate of snowmelt, preventing the torrent of inflow — as in the spring of 2023 — that can rapidly replenish the reservoir.

Mark Ward has seen all those factors affect the reservoir over the decades.

His family uses reservoir water to irrigate crops in the Baker Valley. He’s also a member of the board of directors for the Baker Valley Irrigation District.

Ward said on Tuesday, April 8, that he doesn’t expect the reservoir to rise above about 55,000 acre-feet this year. That would be the most since August 2017, slightly above the peaks of 2023 and 2024, but still only about 75% of full.

Ward said he would appreciate another major rainstorm.