In an August 1, 2024 post, I updated the status of water quality in the Klamath River during the 4-dam removal project. I had several concerns: sporadic turbidity events, dropping flow rates, and higher water temperatures; all of these concerns had been acknowledged in the project’s planning documents.

Final steps to remove dams on the Klamath River in summer 2024, including dumping additional sediment from exposed reservoir reaches, has again raised concerns about water quality in the Klamath River. The problem is that, this time, fall-run Chinook salmon runs to tributary streams like the Scott and Shasta Rivers are at their peaks. Such water quality degradation events, especially during the late summer fall-run Chinook migration season, would normally be considered violations of state and federal water quality standards. However, these events were expected in the monumental 4-dam removal project on the lower Klamath River.¹

Excerpts from NMFS biological opinion (p. 164 of NOAA 2021):

“Effects associated with reservoir drawdown (i.e., SSC and dissolved oxygen impacts) will affect all populations of SONCC coho salmon that utilize the Klamath River during some portion of their life history cycle, while the other short-term effects associated with dam removal, construction, and restoration will primarily be limited to individuals from the Upper Klamath population. Therefore, the proposed action is likely to adversely affect coho salmon from the Upper Klamath River, Shasta River, Scott River, Middle Klamath River, Salmon River, Lower Klamath River, Upper Trinity River, Lower Trinity River, and South Fork Trinity River population units in the short term.”

“Behavioral effects resulting from elevated suspended sediment include alarm reactions, avoidance, and reduced feeding. Cederholm and Reid (1987) found that juvenile coho salmon prefer low to medium concentrations of suspended sediment, and that juvenile coho salmon prey capture success significantly declined at concentrations of 100 to 400 mg/l. Salmonids have been observed to prefer clear over turbid water (Bisson and Bilby 1982), and move vertically near the water surface (Servizi and Martens 1992) and/or downstream to avoid turbid areas (McLeay et al. 1984; McLeay et al. 1987). More than six weeks of exposure to concentrations of 100 mg/L reduces feeding success, reduces growth, causes avoidance, and displaces individuals (Spence et al. 1996).”

“Suspended sediment contributes to turbidity, which also can have adverse effects if excessive. Bisson and Bilby (1982) found that juvenile coho salmon avoided water with turbidities of 70 Nephelometric Turbidity Units (NTU).”

The problem this summer has been the removal of coffer dams, other remaining infrastructure, and further remaining reservoir sediments (Figure 1). The release of oxygen-demanding sediment caused critically low dissolved oxygen levels for several days in late August, from the Iron Gate gage (Figure 2) downstream 30 miles to the mouth of Walker Creek (Figure 3, about midway between the mouths of the Scott and Shasta Rivers). Highly stressful levels of suspended sediment (>300 FTUs) occurred for nearly a week, and also occurred sporadically through September, downstream as far as Orleans (Figure 4). With water temperatures in the river falling through September (Figure 5), the annual run of adult fall-run Chinook salmon was likely occurring (Figure 6).

The risks to coho salmon and juvenile salmon were likely minimal in summer. The coho salmon run occurs in November-December. Juvenile coho and Chinook salmon juveniles begin moving out of the tributaries with the first significant fall or winter rains. The rains will also bring erosion of accumulated sediment that could cause stress and mortality this winter and spring, factors that were also anticipated in project planning/permitting documents.

From KRRC Facebook pages September 2024:

“The breaching of the cofferdam at Iron Gate released fine sediment – predominantly dead algae – from the former reservoir footprint. As this sediment has moved downstream, there have been impacts to water quality in the reaches below Iron Gate. The largest of these impacts has been increased turbidity levels and large reductions in dissolved oxygen concentrations immediately downstream of the Iron Gate dam site. For decades there have been enormous seasonal blooms of toxic blue green algae in the reservoirs behind the Iron Gate, Copco No. 1, and J.C. Boyle dams and millions of cubic yards dead algae settled to the bottom over years. While most of this dead organic matter was flushed downstream during the drawdown when the reservoirs were drained back in January, some remained on the backside of the Iron Gate cofferdam. That sediment was released earlier this week when the river was returned to a free-flowing state with the breaking of the cofferdam.

“As this oxygen starved dead organic matter is flushed out from the former reservoir into the river, it absorbs the oxygen in the water. That leads to a drop in available oxygen for aquatic animals in the river, including fish.

“KRRC continues to monitor the impacts of this pulse of sediment. The intensity of the impacts to water quality has been decreasing as the turbid water moves downstream. The dips in dissolved oxygen have been smaller and shorter in the downstream reaches of the river, as freshwater from tributaries dilutes the sediment in the river.

“Crews monitoring the situation have observed some mortality among fish in the river reach directly below Iron Gate Dam. These impacts are unfortunate but expected following such a drop in dissolved oxygen. Fortunately, we have not seen mortality in returning adult salmon, currently making their way upstream. Crews will continue to monitor the situation, and we will share information as we learn more.

“This is precisely the kind of temporary negative impact that was anticipated and fully analyzed by state and federal regulatory agencies overseeing the dam removal. Scientists and other experts determined that any short-term pain associated with the dam removal activity was worth the long-term gain for the health of the river, native fish species, and surrounding communities. After the Iron Gate cofferdam was broken last week, some parts of the cofferdam remained in place to allow for the removal of diversion infrastructure. KRRC will remove this remaining piece of in-river infrastructure before the project is completed later this month. Following the breach, a significant amount of impounded sediment began to move down-river, but some remains on the backside of the cofferdam segment still in place.

“Taking guidance from the project’s Fisheries Coordination Team, which is comprised of NOAA Fisheries, Karuk Tribe, Yurok Tribe, California Department of Fish and Wildlife, US Geological Service, US Fish & Wildlife Service and other fisheries and water quality specialists, KRRC will implement an assisted sediment evacuation plan in the coming days. Utilizing a long arm excavator to stir up the material, much of the remaining accumulated sediments will be sent downstream slowly in the coming weeks, ahead of the final removal of the what’s left of the Iron Gate cofferdam later this month. The goal of this activity is to remove as much of this material as possible gradually to limit water quality impacts later in the month, when adult salmon will be coming through the river reach directly below Iron Gate. While we have seen adult salmon already entering the river, they are currently downstream of the areas that were most affected by the sediment that has been released with the breaching of the Iron Gate cofferdam.

“The sediment, mostly consisting of dead algae, is non-toxic, and is too water-logged to effectively be removed from the river using machinery, so a gradual release was determined to be the best option to protect incoming salmon. As the sediment is gradually released downstream over the coming weeks, KRRC, Tribes, and public agencies will carefully monitor river conditions to ensure the dissolved oxygen levels are kept at habitable conditions for fish. Because the Klamath is, in general, a sediment-heavy system, it is important to note that Klamath River salmon are adapted to survive with a certain degree of sediment in the river as they migrate upriver to spawn.

Communities down river can expect turbid (murky) conditions to continue for the coming weeks. These conditions are temporary, and this controlled sediment removal is an important activity to protect the salmon currently making their way upstream.
You can see the targeted sediments for removal below. They are darker in color than the dam material and are upstream of the cofferdam on the right hand side of the image.”