The chart below provides total annual fall Chinook redd counts by year from 1991 through 2023. The redd counts are collected from aerial and deep-water surveys conducted by Idaho Power, the U.S. Geological Survey and the Nez Perce Tribe in the Snake River below Hells Canyon Dam and in the listed tributaries.

Total Redd Count By Year

Year	Snake River	Grande Ronde River	Imnaha River	Clearwater Basin	Salmon River	Total
2024	2,272	210	67	1,283	200	4,032
2023	2,202	254	Not surveyed*	1,848	855	5,159*
	*Poor water clarity caused by heavy rain prevented a survey of the Imnaha in 2023.
2022	1,955	114	8	2,022	576	4,675
2021	1,465	384	46	1,526	247	3,668
2020	2,102	201	28	2,013	394	4,738
2019	1,788	57	7	1,022	17	2,891
2018	1,492	158	14	789	14	2,467
2017	1,869	280	15	2,095	10	4,269
2016	1,972	415	29	3,731	35	6,182
2015	3,155	378	83	5,081	142	8,839
2014	2,808	342	103	3,078	42	6,373
2013	2,667	255	38	2,956	31	5,947
2012	1,828	303	85	1,654	34	3,904
2011	2,837	154	24	1,611	60	4,686
2010	2,944	263	132	1,642	8	4,989
2009	2,095	101	36	1,198	34	3,464
2008	1,819	185	68	949	14	3,035
2007	1,117	80	17	718	18	1,950
2006	1,025	41	36	257	9	1,368
2005	1,442	129	36	487	27	2,121
2004	1,709	161	35	630	21	2,556
2003	1,524	84	44	571	18	2,241
2002	1,113	111	72	524	31	1,851
2001	710	197	38	312	22	1,279
2000	346	8	9	184	0	536
1999	373	13	9	184	0	579
1998	185	24	13	78	3	303
1997	58	55	3	72	1	189
1996	113	20	3	69	1	206
1995	71	18	4	20	2	115
1994	67	15	0	37	1	120
1993	127	49	4	36	3	219
1992	47	5	3	26	1	82
1991	47	0	4	4	0	55

Idaho Power’s Fall Chinook Program began in 1991 and is a voluntary operations plan for the Hells Canyon Complex.

The program provides a stable river flow level during the fall Chinook salmon spawning period, generally from mid-October to early December. The flow level provided during the fall Chinook salmon spawning period generally establishes what the minimum flow from Hells Canyon Dam will be once spawning is complete.

Minimum Flows

This minimum flow may be slightly lower than the stable flow provided during the spawning period. The minimum flow depends on the depth of the shallowest redds observed during the spawning period. The minimum flow level is the level that will protect the shallowest redd in the Snake River from being dewatered. Dewatering is when there is not enough water to sufficiently cover the redds.

Idaho Power maintains this minimum flow throughout the entire incubation and emergence period, which is approximately the end of May. The emergence period is when the fish swim up out of the redds. The stable flow level provided during the spawning period may vary from one year to the next. The flow level depends on the quantity of water available, which largely depends on the amount of snowpack within a given water year.

Redd Counts

The U.S. Fish & Wildlife Service and Idaho Power started a cooperative research program to determine the quantity of spawning habitat and flow levels necessary to support sufficient spawning habitat for fall Chinook salmon. As part of this research program, fall Chinook salmon redd counts happen each year.

Redd counts monitor redd locations and establish the location and depth of the shallowest redd. Idaho Power and the U.S. Fish and Wildlife Service do weekly counts during the spawning period over the Snake River. In addition, the Nez Perce Tribe conducts aerial redd counts on the Clearwater, Grande Ronde, Imnaha and Salmon rivers. When the program began, aerial surveys were conducted by helicopter. Now, flights are done with drones that record video and still photography that enable careful analysis to obtain more accurate data while keeping biologists safely on the ground.

These survey flights account for the majority of the redds observed. However, in the Snake River, many redds cannot be observed from the air because they are in deep water. So, deep water redd searches using underwater videography occur during the spawning period as well as the aerial surveys. Redds as deep as 22 feet have been observed in the Snake River using underwater videography.