This article was published on: 11/15/23 11:14 AM
The headwater spring of the Metolius River, which produces the crystal-clear water beloved by both fish and swimming enthusiasts, is experiencing its lowest discharge rates in two decades of record-keeping.
Measurements taken in September show the spring is discharging water at 47.9 cubic feet per second, the second-worst rate in recent history. The discharge rate was only slightly higher than the 47.6 cfs measurement taken in March 2022. These numbers represent a 55% decline compared to the spring’s discharge rate six years ago.
The headwaters of the Metolius River are just one barometer for the health of aquifers that lie deep underground in Central Oregon. Below-average reservoirs are also a reminder that the region is still suffering from drought. But the drought is easing, and the winter months had substantial snowpack, so why is the Metolius still in the doldrums?
Below average precipitation
Last winter’s good snowpack wasn’t enough to turn around the situation for springs because outside of the snowfall, the area didn’t get a lot of rain, said Jeremy Giffin, Deschutes Basin watermaster.
“Last year was great for the ski resorts as most of our precipitation fell in the form of snow, but overall the precipitation was slightly below average, which has happened several years in a row, with many of those years well below average,” said Giffin.
In mid-April, the Upper Deschutes Basin had snowpack that was 171% of normal while precipitation was 93% of normal.
Precipitation has been average or below average in eight of the past 10 years, according to data from the Natural Resources Conservation Service. Central Oregon’s hottest year was 2021 with data going back to 1948. The region’s third hottest year was 2020.
Low-flowing streams and rivers have become common in the Upper Deschutes Basin. U.S. Bureau of Reclamation data shows that the spring inflow to the Deschutes River is 10% below average.
“My thoughts on the (Metolius) spring is that it is following the other trends of major springs here in Central Oregon, which is very low outflow due to prolonged drought,” said Giffin.
The dip in spring discharge has had a corresponding impact on the river. According to data compiled by the Oregon Water Resources Department, the median flow in the Metolius River, as registered at a gauge in Camp Sherman, shows a drop from 320 cubic feet per second in 2012 and 2013 to around 200 cfs in 2022 and 2023.
Impacts on fish
The headwater spring of the Metolius is an area of scenic beauty, and each summer it attracts visitors who come to marvel at the clear water surfacing from the aquifer. The low discharge may be disappointing for the repeat visitors to the area who can recall the spring releasing more water. But spare a thought for the fish and other aquatic species who need to make a home in the low-flowing Metolius.
The headsprings and spring-fed tributaries to the Metolius create important spawning grounds for chinook salmon, bull trout, redband trout and kokanee. These fish require consistent sources of cold and clear water to complete different stages of their lives, explains Jerry George, a fish biologist with the Oregon Department of Fish and Wildlife.
George said shallower conditions in the Metolius caused by low discharge reduce the amount of suitable habitat for adult fish to spawn and juvenile fish to survive from predators and disease.
The low discharge rate favors birds, otters and other predators who can catch fish more effectively when river levels decline, he said.
“In some areas where fish must navigate small waterfalls and chutes to reach spawning grounds, reduced streamflow can create impediments to fish passage and limit areas fish can access,” said George.
Redband trout redds in decline
The drought and decreased discharge levels have not impacted bull trout numbers yet, but studies have shown a small decline in redband trout nests, known as redds, from 2018 to 2021 numbers, according to ODFW.
“It is unclear if the recent decline in redband trout redd counts is a direct result of reduced streamflow or a combination of factors, but the low water conditions are certainly a disadvantage,” said George.
Large-bodied spring-run chinook salmon are perhaps the most affected by low streamflow in the Metolius. Due to their size they may have to navigate shallow riffles and spawn in less-than-ideal conditions with their backs out of the water.
“This can attract predators and requires fish to expend excess energy that can lead to fish dying prematurely before spawning,” said George.
It could be some time before Metolius-dwelling fish get a reprieve from the low water situation, experts caution.
Joe Kemper, a hydrologist with the Oregon Water Resources Department, said groundwater levels and spring discharge aren’t impacted by a single season of good or bad precipitation numbers but instead track five-year trends in precipitation.
“The Deschutes Basin has had below-average precipitation for five of the last six years,” said Kemper. “It will take several sequential years of above-average recharge to counter that deficit.”