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Source: Global Science
Author: Huang Yujia
Image credit: pixabay
The fish are so tired.
In September 2002, residents living in the lower reaches of the Klamath River in the United States noticed a sudden large number of dead fish appeared near the river. The U.S. Fish and Wildlife Service (USFWS) and related organizations quickly conducted an investigation and found that while there was a wide variety of fish species that died, it was mainly the adult hook salmon (Oncorhynchus tshawytscha), which accounted for more than 97 percent. The USFWS conservatively estimates that at least more than 30,000 hookfish, or nearly 20 percent of the total number of such fish in the river, died in the accident. Some organizations even believe that the actual number of salmon killed may be more than 70,000.
Investigators found that the dead fish showed clear signs of illness: gill necrosis, bacterial growth, sores, anal bleeding and ulcers. The investigation found that the fish died from infection with Ichthyophthirius multifiliis and Flavobacterium columnare.
克拉马斯河下游出现的大量死鱼（图片来源：California State Water Resources Control Board）
The multi-child melon worm is a parasitic ciliate that is found all over the world. When the water temperature is high, the fish density is high, or the fish are stressed, the parasite can multiply and cause disease in the fish. At the same time, these factors may also lead to the growth of Flavobacterium columnaris in abundance. Indeed, there were 12 days with high maximum water temperatures in the two weeks leading up to the concentrated death of these fish. However, the average water temperature did not increase significantly in this year compared to earlier years, and it has never been the case before, indicating that temperature is not the main factor.
Salmon is a type of fish that migrates through the river. In the summer, juvenile salmon cross the Klamath River and enter the sea from freshwater waters. After a year or even several years, when they reach sexual maturity, they return to their homeland along the Klamath River and begin to lay eggs and reproduce. The multi-seeded melon worm is a parasite that can only survive in a freshwater environment, and the seawater will kill it directly. Therefore, the death of a large number of salmon due to it can only occur if the salmon stay in freshwater waters for a long time.
The researchers found that the 2002 salmon migration was significantly delayed compared to previous years, and that they stayed in the lower Klamath River for more than 20 days, resulting in a significantly higher salmon density that year, making them more stressed and more susceptible to infection. But why did the regular migratory salmon suddenly change their pattern this year? Eventually, the researchers zeroed in on the Iron Gate Dam on the Klamath River.
Ranking order of average flow at the Iron Gate Dam from 1981 to August 19 to September 27, 2002 (Image source: California State Water Resources Control Board)
In 2001, the Hoopa Boat Dance festival was held by opening the floodgates of the Trinity River upstream, resulting in a short-term flow of the downstream Klamath River, which may have led to a large production of salmon spawning. By 2002, a large number of salmon had migrated there, and due to the low volume of water that year, the Iron Gate Dam did not increase the flow of salmon according to the salmon situation. In fact, this year's flow was the second-lowest in nearly 20 years, resulting in a large number of salmon stranded here. This, coupled with a series of external conditions such as the right water temperature, eventually led to a large number of salmon deaths.
If the Iron Gate Dam had increased its flow rate, perhaps such a tragedy would not have occurred. Therefore, this accident can be regarded as a "man-made disaster".
Demolition of the dam
Even before this incident, many local residents had been calling for the removal of dams on the Klamath River, as they threatened the normal breeding of migratory fish, destroyed the culture of local tribes, and affected water quality. For example, due to the restricted flow of river water, cyanobacteria begin to multiply in large numbers, not only producing toxins, but the dead cyanobacteria also consume oxygen in the water, affecting other organisms in the river water.
The Klamath River was once the third-largest source of salmon on the West Coast of the United States, but since damming it began in the early 20th century, the population of migratory fish such as salmon has greatly declined. Not only is this because the dam blocks the breeding route for migratory fish such as salmon, but the lower dam outfall can also cause the dam to be too cold in the summer and too hot in the fall, which is also detrimental to fish survival.
In addition, the construction of dams affects the river's ability to carry sediments such as sediment, resulting in the deposit of larger particles such as sand and gravel at the upstream end of the reservoir to form a delta, while fine sediment accumulates in the reservoir. This not only poses a hidden danger to the reservoir, but also leaves the downstream rivers deprived of sediment. At the same time, when the water flow is released from the reservoir, it erodes the riverbed downstream, destabilizing the riverbank. Less sediment in rivers leads to further sediment scarcity in coastal areas, which in turn leads to erosion of land by seawater.
大坝上游端会形成三角洲（图片来源：California State Water Resources Control Board）
In the wake of the massive fish kills, more residents and institutions have joined the wave of opposition to the dam. They proposed the Klamath Basin Restoration Agreement, which calls for the restoration of most of the Klamath Basin's riparian zone, the removal of dams on the Klamath River, and the guarantee of irrigation water for local residents. Although the agreement failed to legislate, in 2016 they bypassed the U.S. Congress and formed the Klamath River Renewal Corporation, which specializes in removing dams.
They were to dismantle four dams on the Klamath River, from upstream to downstream. C. John C. Boyle Dam, Copco No. 1 Dam, Copco No. 1 Dam, and Iron Gate Dam. Today, they generate less than 2% of the electricity of PacifiCorp, a utility serving the western United States, due to problems such as declining river levels. In November 2022, the U.S. Federal Energy Regulatory Commission (FERC) officially approved the world's largest dam removal and river restoration project to date, with four dams adding up to more than 120 meters of vertical height and an estimated cost of $500 million, to be shared by companies in California, Oregon and Pacific.
In June 2023, the smallest of the four dams, the Koppke 2 Dam, began to be dismantled and completed in October of that year. In January this year, people began to dismantle the remaining three dams, which are expected to be completed this year.
Killed again
On January 9, 2024, the Iron Gate Dam opened its gates to release water. In February, the California Department of Fish and Wildlife Management (CDFW) released 830,000 salmon fry into tributaries upstream of the Iron Gate Dam before the dam was completely removed, in the hope that the small fish would be a mainstay in restoring the Klamath River salmon population. However, it soon became clear that hundreds of thousands of fry had died.
At first, there were concerns about whether the demolition of the Tiemen Dam had caused a change in water quality, as the reservoir had brought a lot of silt and decaying algae downstream, making the river muddy. But investigators did not detect significant changes in water quality, and salmon downstream of the dam were business as usual.
Salmon fry (Image source: CDFW)
Investigators found that the dead fry had a bulging eyeball, typical of gas bubble disease. This can occur when the water pressure is too high, saturating the water with gases such as oxygen. Therefore, they speculated that the sudden change in water pressure caused by the release of water from the dam changed the gas content in the river water, causing the death of juveniles as they passed through the tunnel of the Tiemen Dam.
However, CDFW staff said the problem was only temporary, and that when the dam and associated facilities were completely dismantled, things would return to normal. And, with the release of sediment from the reservoirs, the Klamath River will continue to become turbid in the coming months, and dissolved oxygen levels will drop, threatening to kill more fish. Except for the accidental death of this batch of fry, the rest was within their expected range.
If the model is correct, the Klamath Basin is expected to recover to 80 percent of its former levels within the next 30 years, and the catch of the ocean will increase significantly. Seeds of local species are being sown in the drained reservoir in anticipation of restoring the basin's pristine ecology.
This may be a glimmer of hope hidden behind the tragedy after tragedy.
Reference Links:
https://www.waterboards.ca.gov/waterrights/water_issues/programs/bay_delta/california_waterfix/exhibits/docs/PCFFA&IGFR/part2/pcffa_155.pdf
https://www.americanrivers.org/2023/06/6-things-you-need-to-know-about-the-klamath-river-dam-removals/
https://apnews.com/article/business-california-native-americans-dams-salmon-311ea96fda0fe1b0052ab8cef9ae36a9
https://arstechnica.com/science/2024/01/the-largest-us-dam-removal-effort-to-date-has-begun/
https://wildlife.ca.gov/News/Archive/fall-run-chinook-salmon-fry-succumb-to-gas-bubble-disease-in-klamath-river
https://w.spcranic.com/California/Article/Klameth-Dames-Salman-tie-of-18700078.PF
https://www.theguardian.com/environment/2024/mar/05/salmon-klamath-river-dam-removal-project
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