Why we probably can’t dredge Upper Klamath Lake

If landowners, scientists and government agencies can improve the water quality in Upper Klamath Lake (and, consequently, life for endangered suckers), it could take a great deal of pressure off water management in the Klamath Basin.

But how do you rehabilitate the largest body of freshwater west of the Rocky Mountains? At 96 square miles, it’s difficult to implement any fix at the scale and swiftness needed to make measurable water quality improvements in Upper Klamath Lake before its suckers go extinct. Because hundreds of millions of federal funding dollars were recently earmarked for environmental restoration activities in the basin, some people have asked, “Why not dredge it?”

Dredging water bodies has been used for decades around the world to achieve a variety of objectives, from deepening lakes to removing polluted sediment. Theoretically, it could do both of those things in Upper Klamath Lake, increasing available storage for irrigation diversions and river flows, while also removing some of the nutrient-rich sediment that fuels its algae blooms.

However, sucking up sediment from a lakebed is extremely expensive ($460 million is the current ballpark figure) and can result in unwanted environmental side effects. The latest scientific literature does suggest dredging can be successful, but mainly in lakes that are small and don’t experience consistent pollution from external sources.

“Upper Klamath Lake meets neither of these criteria,” said Megan Skinner, water quality specialist for the U.S. Fish and Wildlife Service office in Klamath Falls.

Prior to colonization, it’s likely that Upper Klamath Lake was no Tahoe. The lake is naturally eutrophic, or high in nutrients like nitrogen and phosphorus. This environment may not yield the clearest water, but it provides the foundation for a robust aquatic food chain. Nutrients grow aquatic plants and microorganisms, which would fuel invertebrates and fish.

The problem now is that there’s too many nutrients entering the lake from its tributaries, released into the watershed by logging, grazing, stream channeling and irrigation practices. Rivers erode more sediment than they used to, sending excessive amounts of phosphorus directly into Upper Klamath Lake and fueling the domination of toxic cyanobacteria in the water. Thanks to this external loading, researchers now consider Upper Klamath Lake “hypereutrophic.”

The Oregon Department of Environmental Quality evaluated where this excess phosphorus was coming from in the early 2000s. Approximately 60% in a given year comes from the lake’s own sediments, while 40% enters it from its watershed, including tributaries and lands adjacent to the lake. ODEQ found human activities responsible for 40% of that external load, mostly through land use changes along the tributaries. ODEQ set total maximum daily load (TMDL) requirements for Upper Klamath Lake in the early 2000s, requiring a reduction of 40% in external phosphorus.

Skinner has been fielding ideas to improve water quality in Upper Klamath Lake for several years. They range from long-term restoration — such as de-channelization, riparian planting and fencing and spring reconnection —  which counteracts the underlying issues of sediment loading. She said other ideas amount to what she calls “techy quick fixes,” which attempt to alleviate symptoms in the short-term.

The latter category might buy the C’waam and Koptu some time but, at worst, could suck away precious resources that may be better spent on tackling the core of the problem.

“One issue I often run into with these types of projects is scale. What works and is cost effective in a 2-acre lake may cost hundreds of millions of dollars and require monumental effort in a lake as big as Upper Klamath Lake,” Skinner said.

Dredging is one of those “techy quick fixes” that sounds better than it actually is, at least in this watershed. It may improve things from a water storage standpoint, but it would easily be counteracted by the continuous loading of excess phosphorus from outside the lake. Plus, it would be prohibitively expensive.

“It may not be the quick fix people would hope,” said Jacob Kann, an aquatic ecologist with Aquatic Ecosystem Sciences LLC. “In a shallow, large lake like Klamath, it’s very difficult to actually treat symptoms.”

Hydraulic pipe dream

Upper Klamath Lake has been dredged before, mainly for boating and logging operations and to build dikes in the early 20th century. But none of those operations occurred at the scale necessary to positively influence lake depth or water quality. Dredging for those purposes has been brought up since at least the 1970s, when the Army Corps of Engineers evaluated ways to fix the lake’s declining health.

“Lake deepening may feasibly alter lake morphometric characteristics in a manner that will reduce algal productivity. Whether the reduction would be sufficient to justify project implementation on the basis of water quality benefits alone is highly questionable,” the Corps wrote in a 1982 report.

After 40 years, the scientific consensus around dredging hasn’t changed much.

Kann said dredging has been part of the conversation since before he began working in the Klamath Basin. The main issue is the influence of external phosphorus on water quality dynamics in the lake. If that isn’t taken care of, the benefits of dredging would only be temporary before becoming eclipsed by an onslaught of new sediment.

But why not dredge to buy the fish some time while we fix the watershed, if removing some phosphorus contained in the lake’s sediment might dampen the severity of the algae blooms? Kann said he hasn’t ruled that out entirely, especially if a project were to focus on smaller phosphorus “hotspots” in the lake, whose sediments contain especially high nutrient concentrations.

A workshop of scientists convened in 2010 by the Klamath Hydroelectric Settlement Agreement, which contains provisions for water quality work in the Upper Klamath Basin, evaluated a list of activities to improve the situation in the lake, including dredging. In a report released in 2013, the workshop participants concluded that dredging may be “generally effective” at phosphorus removal and subsequent water quality improvements.

Additionally, the report pointed out that the removed sediment could help restore depleted soils on agricultural lands or rebuild the lake’s drained fringe wetlands primed for restoration, most of which have subsided following decades of agricultural use.

However, the workshop concluded that dredging the entire lake would be infeasible, costing as much as $460 million and removing an obscene amount of sediment that would all have to go somewhere else. Even a pilot project identified near Goose Bay, south of the Williamson River Delta, which would dredge only 15 acres worth of sediment, would cost roughly $1 million.

And there’s still the tens of thousands of acres worth of phosphorus in the rest of the lake that would remain untreated, not to mention the potential direct impacts to suckers and their habitat — the very species scientists are trying to save.

“Dredging is just expensive and tricky, and I think the benefits were pretty nebulous,” said Maia Singer, senior scientist at Stillwater Sciences, which produced the 2013 report. “It was among the most expensive things we looked at.”

Singer said the main benefit to “hotspot” dredging similar to the pilot project would be to acquire sediments to counteract subsidence during wetland restoration projects. That water quality workshop report was a major nail in the coffin for discussions about dredging, at least in the scientific community working on the basin.

“I don’t think anybody’s looked seriously at dredging since then,” Singer said. “In general, the consensus is that it’s very expensive and a real longshot.”

But could removing the years of sediments that have already accumulated in the lakebed give us a head start while we restore its tributaries? Kann said his recent research on sediment loading in Upper Klamath Lake suggests that the lake’s “internal loading” may actually be highly influenced by external loading. Therefore, directly removing sediment from the lake may be more of a Sisyphean task than previously thought.

Phosphorus has its own seasonal cycle in the lake. Total phosphorus measurements in the water column begin to climb in May or June and peak in July or August, after which they spend the fall, winter and spring falling until the process restarts. During the winter, when plants and algae are mostly dormant, the phosphorus settles into the lake’s sediments until warmer temperatures release it in the spring, making it available to cyanobacteria during the growing season.

Kann’s research in 2020 for the U.S. Fish and Wildlife Service found a strong correlation between winter phosphorus loading, phosphorus retention in the lake’s sediments and phosphorus outflow from the lake during the late summer. Basically, the more phosphorus-rich sediment that entered the lake at the beginning of the water year, the more would release into the water column during the algae growing season.

Kann said that relationship wouldn’t be as coupled if the lake’s “legacy phosphorus,” or the nutrients left over from decades of sediment accumulation, were primarily driving the cycle. Therefore, dredging the lake to achieve water quality objectives would be akin to getting liposuction to lose weight without changing your diet: Excess phosphorus would continue to pour in from the lake’s tributaries each winter, theoretically requiring it to be re-dredged every year.

Instead, Kann said simply ramping up efforts to restore the Williamson, Sprague and Wood rivers and reduce that external loading at its source may have more lasting, cost-effective benefits than dredging. And, thanks to his research, the fruits of that labor may even appear in the short term, too.

Kann said this analysis is still largely consistent with previous modeling by the U.S. Geological Survey, which suggests that it would take Upper Klamath Lake 20 years to return to its historical equilibrium after the TMDL is reached in the watershed. Those models actually show that 80% of the phosphorus reduction in the lake occurs within the first five years of reining in pollution, he said.

“These newer analyses show that the lake really does respond quite rapidly to changes in the inflow phosphorus concentration,” Kann said. “That means we need to put the effort there and try to increase the scale of phosphorus reduction in the watershed as rapidly as we can.”

Other focuses

Stakeholders have to be careful with how they spend limited funding on restoration in the Klamath Basin.

The more than $160 million appropriated by Congress over the next five years isn’t enough to accomplish any one thing, whether it’s dredging Upper Klamath Lake or restoring every mile of the Sprague River. Especially given how close C’waam and Koptu are to becoming functionally extinct in the wild, people have to balance long-term fixes with short-term relief — or choose between them.

Clayton Creager, watershed stewardship coordinator for California’s North Coast Regional Water Quality Control Board, said that, at this point, enough research and planning has gone into tributary restoration that he’d hesitate to spend more money evaluating short-term fixes like dredging — especially when it would take so many years to acquire that funding, design a project and get it permitted that it would cease to be a quick fix altogether.

“We’ve made enough progress on the long-term, and the funding discussions appear adequate to support the long-term, that the value of short-term fixes relative to the potential for long-term fixes — the equation has significantly changed in the last couple of years,” he said.

Creager said that could change in a couple years if stakeholders are unable to make significant headway along restoring the Sprague and Williamson rivers, which involve numerous partnerships with individual landowners. But the recent research suggesting that external phosphorus removal would make a difference in the short term may mean everyone can have their cake and eat it, too.

“I’m so hopeful for the long-term process stuff at this point,” Creager said.

Still, there may be measures less disruptive or expensive than dredging that could help make life easier for suckers as partners work to clean up the watershed. Skinner said she’s already crossed quite a few off her list, but she’s still evaluating activities like killing cyanobacteria cells directly with ultrasound waves or UV radiation, or using oxygen or a compound called Phoslock, which bounds to phosphorus atoms and renders them useless to algae.

Oxygenating the lakebed would also increase dissolved oxygen levels for suckers during sharp, cyanobacteria-driven declines in the summer that likely contribute to their stress and eventual death.

But because Upper Klamath Lake is so big, these interim solutions have to target the suckers themselves instead of the entire lakebed. Fish biologists have made progress on tracking the movement of C’waam and Koptu beneath the surface to figure out where they tend to congregate at different times of the year, but the dynamics of the juvenile die off at the end of each summer remain somewhat of a mystery.

“I am always looking for new ideas and therefore encourage readers to reach out if they have any ideas for me to explore,” Skinner said. “I will consider anything and everything.”

Singer agreed that the basin won’t get anywhere without fixing the underlying problems in the Upper Klamath Lake watershed, but the discussions about dredging or any quick fix underscore just how dire the situation is for suckers. Without some way to keep the species alive in the interim, would water quality improvements from tributary restoration arrive in time?

“I think it’s important to focus externally, but I still wonder if there’s a way to just, you know, get some oxygen to the poor fish,” she said.