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The kill ocurred from Sept 18-Oct. 1, 2002. It did rain, but the post-mortem did not attribute a lot to that. There was, however, and increase of flows on the Trinity followed by a decrease prior to the kill. http://www.earthjustice.org/library/references/fishkillfwscauses.pdf :
pg 13
“Precipitation
During the months of August through October 2002, rainfall amounts were low across the Klamath Basin at the stations surveyed (Figure 5). No precipitation was recorded at the mainstem stations of Weitchpec and Hoopa, or the Salmon River weather station. The only significant rainfall occurred at the Klamath weather station on September 18, 2002, when 0.35 inch of rain fell. Lesser amounts of rainfall were recorded infrequently in the upper basin within the Shasta and Scott River drainages. Rainfall amounts measured in the lower basin were lower than longterm
averages (Figure 6). Therefore, we conclude that August and September precipitation did not significantly contribute to discharges in the lower Klamath River, and flows were primarily dependent on upstream and tributary discharges.”

River Discharges
Mainstem Discharges, August through October 2002 Iron Gate Dam represents the upper limit of anadromous fish migration in the Klamath Basin (PacifiCorp 2000). Discharges are measured at a USGS gage located below the Dam at Klamath
River mile 189.8. During the months of August and September, River discharges below Iron Gate Dam were fairly constant (Figure 7). Average daily discharges during August and September were 666 cfs and 813 cfs, respectively. The mean daily average discharge was 760 cfs until September 27, 2002. On September 27, a pulse flow was released from Iron Gate Dam in an effort to increase the volume of flow through the die-off reach to reduce crowding, and to stimulate fish to begin upstream movement (McInnis 2002, McCracken 2002). Ramping from 767 cfs to 1,350 cfs occurred over a 2-day period. This discharge was maintained through October 9, 2002, after which discharges declined to 885 cfs by October 13, 2002. This resulted in an additional 36,000 acre-feet of water provided over a 2-week period. October discharges averaged 882 cfs after the pulse flow subsided.”

“Tributaries, August through October 2002 The three major tributaries that discharge into the Klamath River between Iron Gate Dam and the confluence of the Trinity River are the Shasta (Klamath RM 176.6), Scott (Klamath RM 143),
and Salmon Rivers (Klamath RM 66) (Figure 1). During August the mean discharge from the Shasta River was 23.9 cfs (Figure 7). During September, the average discharge increased to approximately 31.8 cfs with a small increase in
discharge occurring September 7 to 13, 2002. Discharge increased significantly between September 27 and October 9, 2002 from 33 to 149 cfs. This increase coincided with the end of the irrigation season within the Shasta River watershed.

Scott River discharges were measured at the Fort Jones gage. This gage is located upstream of the confluence with the Klamath River (Klamath RM 143) on the Scott River (Scott RM 21) (Figure 1). Consequently, this gage does not capture the entire discharge of the river, particularly lower River accretions. Scott River discharge was even lower than Shasta River discharge during August and September (Figure 7). The Scott River exhibited a mean discharge of 14.9 cfs during
August 2002. September discharge was lower with a mean of 11.5 cfs. Discharge was fairly constant and gradually decreased from August through September.

Salmon River discharge was measured at the USGS gage near the mouth (Figure 1). Salmon River discharge declined from about 271 cfs starting on August 1, 2002 to about 119 cfs on
September 30, 2002 (Figure 7). The mean monthly discharges for August and September were 171 and 124 cfs, respectively. Small increases in discharge were observed on September 8 and 19, 2002.

The Trinity River is the largest tributary of the Klamath River (Figure 1), emptying into the Klamath at river mile 43.5. Discharges are primarily regulated in the lower Trinity River by Lewiston Dam located on the Trinity River at river mile 111. Lewiston Reservoir serves as an
afterbay to the Trinity Powerplant and regulates releases into the Trinity River and diversions to the Sacramento River basin.

During August and September 2002, the mean monthly discharges were 471 and 454 cfs, respectively, below Lewiston Dam (Figure 7). Daily average discharges were fairly constant. From September 5 to 20, 2002, daily average discharge declined from 485 to 440 cfs.

The Hoopa gage is located on the Trinity River at river mile 12.4, and is the primary measure of total discharge of the Trinity River into the Klamath River (Figure 1). Mean monthly discharges measured at the Hoopa gage were 696 and 631 during August and September 2002, respectively.
During this time period daily average discharge gradually decreased from 760 to 609 cfs (Figure 7). However, daily average discharge increased between September 5 and 9, 2002, from 636 to 693 cfs. Discharge slowly declined to 638 cfs by September 12, 2002, and thereafter.