Environmental Assessment. 2013 Lower Klamath River Late-Summer Flow Augmentation from Lewiston Dam

In August and September 2002, an estimated 170,000 fall-run Chinook salmon returned to the Klamath River, and a substantial number of adult Chinook salmon and other salmonids died prematurely in the lower Klamath River. This included an estimated 344 coho salmon listed as threatened under the Endangered Species Act (ESA). Federal, tribal, and state biologists studying the die-off concluded that: (1) pathogens Ichthyophthirius multifiliis (Ich) and Flavobacterium columnare (Columnaris) were the primary causes of death to fish; and (2) warm water temperatures, low water velocities and volumes, high fish density, and long fish residence times likely contributed to the disease outbreaks and subsequent mortalities (Guillen 2003; Belchik et al. 2004; Turek et al. 2004). Flows in the lower Klamath averaged about 2,000 cubic feet per second (cfs) during September 2002.

In 2003, 2004, and 2012, predictions of large runs of fall-run Chinook salmon to the Klamath River Basin and drier than normal hydrologic conditions prompted Reclamation to arrange for late-summer flow augmentation to increase water volumes and velocities in the lower Klamath River to reduce the probability of a disease outbreak in those years. Thirty-eight thousand acre-feet (TAF) of supplemental water was released from Trinity Reservoir in 2003, and 36 TAF in 2004, and 39 TAF in 2012. While documentation of the effectiveness of these events is limited, general observations were that implementation of the sustained higher releases from August to early September in each year coincided with no significant disease or adult mortalities.