Study of Summer Whitewater Releases and Macroinvertebrates Finds Little Effect

A just-completed study that included two seasons of field sampling on the North Fork Feather River and two years of analysis shows no ecosystem-level effect of limited summer whitewater boating releases on aquatic macroinvertebrates (insects).

The study was designed by top experts on aquatic insects.  It was commissioned by the Rock Creek – Cresta Ecological Resources Committee, which oversees implementation of the license for the Rock Creek – Cresta hydroelectric project on the North Fork Feather. The license was issued to Pacific Gas & Electric Company in 2001 by the Federal Energy Regulatory Commission. PG&E funded the study.

The study provides scientific answers to concerns that arose among a segment of the angling community about the effects of summer whitewater flow releases on aquatic macroinvertebrates. While this issue generated a level of emotion that divided many anglers, led to the formation of new organizations, and saw some anglers and their representatives vilifying whitewater boating and boaters, this definitive study provides scientific answers to those issues that concerned all of us.

As a result of the study, the Ecological Resources Committee, including CSPA, is considering a proposal to maintain summer whitewater boating releases on the NF Feather below Rock Creek Dam at about the same limited level that has been in effect since 2007.

RCC_Rec Rel Flow Macro Report_2007 Figures

RCC_Rec Rel Flow Macro Report_2008 Figures

RCC_Rec Rel Flow Macro Report_2007 Tables

RCC_Rec Rel Flow Macro Report_2008 Tables


The 2000 Rock Creek – Cresta Settlement Agreement formed the basis for the new 2001 FERC license for the Rock Creek – Cresta Project. The Settlement and the license included a series of summer flow releases from both Rock Creek Dam and Cresta Dam for purposes of whitewater boating. Boating releases were initially scheduled for once a month (June through September or October) on each stream reach. These releases were to vary in magnitude from 800 to 1600 cfs. The Settlement provided the potential for increased number of boating release days based on monitoring of actual numbers of boaters using the resource. However, as a prerequisite to increases in the number of boating releases, the Settlement also contained a provision that required the Ecological Resources Committee (“ERC,” composed of Settlement signatories) and the Forest Service[1] to determine that boating flows were not having significant adverse impacts on aquatic resources.

Beginning in 2002, the ERC defined and commissioned studies to evaluate the impacts of summer boating flows on macroinvertebrates and fish stranding. The first year of study by Garcia and Associates (“GANDA”) evaluated the number of insects drifting in the current as the boating flows were released. A number of parties criticized this approach: while increased flows clearly increased the numbers of drifting insects, the significance of this episodic increase was completely unclear. Perhaps most damaging was the use in the report of the term “catastrophic drift.” There was technical disagreement over whether the term applied to the conditions during boating releases, but more importantly the term evoked an emotional response that by its very nature prejudiced the outcome of any evaluation.

The ERC changed studies by GANDA in 2003 and 2004 to evaluate the number of insects present in the river before and after the flow releases, rather than drift during the releases. Two years of study showed no significant changes before and after releases. There were changes over the course of the season, but the studies were not designed to evaluate seasonal changes.

There was considerable disagreement on the results of the 2003 and 2004 studies. Commenters cited several issues, especially the lack of appropriate comparison reaches. They also raised concerns about lack of hydrologic analysis, lack of historical context, and lack of ecosystem synthesis. Notable in the latter was disagreement over the meaning of changes in the macroinvertebrate populations: it was unclear whether lower numbers of insects in September as compared to July were the result of boating flow releases, or whether this reflected a seasonal variation that had different causal factors.

Perhaps the greatest concern was the failure of the study design to define a sufficient number of hypotheses and to define thresholds of significance before field sampling took place.

No agreement about the meaning of the results of the 2002-2004 macroinvertebrate studies emerged. 2006 began with an ERC that was divided to the point that several participants suggested that consensus on boating was not achievable. Several entities in the ERC reduced their participation, and one NGO ended its participation altogether.

At the end of 2005 and throughout 2006, CSPA and American Whitewater (AW), with the participation of the coordinator of the California Hydropower Reform Coalition, conducted a long-term negotiation about the future of whitewater boating releases on the NF Feather River. In addition, on the Cresta reach in 2006, only four foothill yellow-legged frog (FYLF) egg masses were found, and only two of these egg masses survived to produce tadpoles. In late June of 2006, a combination of large spills and a dramatic decline in flow due to operation of Poe Dam caused the mortality of 43 out of 83 FYLF egg masses on the Poe reach of the NF Feather, just downstream of the Cresta reach. This mass mortality (unfortunately followed by a similar event in 2011) highlighted both the vulnerability of FYLF to flow fluctuations, and also the fact that factors other than boating releases were often the immediate cause of frog mortality. Nonetheless, because of the severely depressed number of egg masses on the Cresta reach, the Forest Service cancelled boating releases on Cresta in 2006, 2007 and 2008.

By the end of 2006, CSPA and AW were thus suddenly down to negotiating boating flows on one stream reach, the Rock Creek reach of the NF Feather, downstream of Rock Creek Dam.[2] CSPA made the tough decision to agree to an interim three year period with a limited increase in the number of boating days on the Rock Creek reach; at the advice of a macroinvertebrate expert, these releases were to be staged on consecutive days. AW agreed to use some of the water devoted to boating flows to keep the flows up overnight, changing two short high flow events into one longer but lower magnitude high flow event.


As another condition of agreeing to these interim boating flows on the Rock Creek reach, CSPA insisted that ERC commission a definitive study of the effects of summer boating flows on macroinvertebrates. CSPA and AW approached PG&E to provide funding. For the study to be definitive, it required up-front buy-in from the entire ERC and the Forest Service on study design, and close consultation on the execution. Further, it required experts involved in the study: the ERC chose Rick Hauer of Montana State University and Vince Resh of the University of California, two of the preeminent macroinvertebrate experts in the world, to design the study. Hauer and Resh also oversaw the study’s implementation.

One of the main elements that had been missing in the GANDA studies was made simple by the cessation of boating flow releases on the Cresta reach: Cresta became a control (comparison) reach. Cresta is of course greatly similar to the Rock Creek reach; as such, most variables other than the response of insects to boating flows were eliminated. In addition, a portion of the Belden reach of the NF Feather, directly upstream of Rock Creek Reservoir, was used as a second control reach.

Consultant Entrix completed the field work 2007 and 2008, and initial report preparation in 2009. In 2010, the Forest Service recommended additional statistical analysis in the report, which improved the document but delayed its completion. In early 2011, a draft report was released to the ERC. CSPA and AW provided comments in April, 2011. The final report was issued in December, 2011.

The study plan for the field work and report included testable hypothesis using indicator taxa, and differentiated the effects on functional feeding groups. It set a level of significance at a threshold of 50% change at a 95% confidence level. This relatively conservative level of significance was chosen in part because of acknowledged variability in insect density and the relatively limited frequency of sampling.

The study as described in the report found that the existing level of whitewater boating releases on the Rock Creek reach caused did not cause ecosystem-level effects on macroinvertebrates. This is the big picture, take home message. After boating releases, there was no less food for trout.[3]

Some individual taxa (insect species) did show statistically significant differences between the “treatment” reach and the control reaches. In some cases, taxa on the Rock Creek reach showed greater numbers after boating flows, at a level that was statistically significant. In some cases, taxa on the Rock Creek reach increased after boating, but did not increase as quickly as did the same taxa on control reaches in the same time period; in almost all such cases, gross numbers increased, but in some cases the difference in the rate of increase compared to one control reach was deemed statistically significant.


Overall, food production for trout is unaffected by whitewater boating flows.

During whitewater releases on the Rock Creek reach of the NF Feather in 2007 and 2008, some taxa of aquatic insects were affected. None was affected consistently. The error bars are very wide, because there is a relatively small sample size and because aquatic insect populations vary dramatically from year to year. If there is a statistically significant reduction in four taxa at different times, but not consistently, when other taxa increase and when overall food production is unchanged, does that warrant a management change?

We don’t think so. We think we’ve hit the right level of compromise. There will be some who say that we should stop an activity if it has any effect. We disagree. The action has to be appropriate to the degree of effect. Consider for a moment what we might be looking at if we applied the standard that any effect on insects required cessation of an action, and then someone else applied the same standard for frogs.

Some frog scientists believe that FYLF do better in streams with very low summer flows and high water temperatures. We have FYLF on the Cresta reach. Water temperatures are too high for trout, but close to the range deemed optimal or frogs. Reducing flow in the summer might produce an incremental benefit for frogs. Of course, that would make conditions for trout even worse than they are, contrary to the  Rock Creek – Cresta license, which says we increase flows when the water is too warm for trout. Because it might improve conditions for frogs, do we stop our management actions on the NF Feather to increase summer flows for trout protection?

We believe we have struck the right balance on the NF Feather. The existing frequency and magnitude of boating flows on the NF Feather may have a very small level of effect on aquatic insects. We are holding the line there, and are monitoring in the future for long-term effects on those bugs that seem to be have been affected in 2007 and 2008.

Part of our calculus is that the culture of leaders of the whitewater community has changed. Summer releases explicitly for whitewater boating are no longer the paradigm for American Whitewater in California. Following the concerns about frogs on the Cresta reach in 2006, AW began development of a new approach to whitewater boating on Cresta. The approach maintains higher flows suitable for boating in June and July, similar to the pattern of the natural hydrograph. This approach was quantified and memorialized in a FERC license amendment for the Rock Creek – Cresta Project in 2009. This approach has also been adopted by AW as a default approach in ongoing relicensings in California. CSPA has supported AW in this welcome change; flows that gradually recede from peak snowmelt are good for frogs and fish, and especially for aquatic insects, as well as for boating.


In consideration of the December 2011 Rock Creek – Cresta Recreational Release Flow Macroinvertebrates Study Report, CSPA and AW have presented a proposal to the ERC for summer boating releases on the Rock Creek for the next twenty years. This proposal would maintain about the same level of boating releases that the macroinvertebrate study analyzed in sampling in 2007 and 2008. PG&E has agreed to perform targeted analysis of  required monitoring of aquatic insects to confirm that this level of boating releases has no long-term effects on individual insect taxa. AW has agreed to accept PG&E funding of access improvements just downstream of Rock Creek Dam in lieu of possible increase of the number of boating days.

CSPA has agreed to the continuation of about the existing level of summer whitewater boating on Rock Creek reach. We recognize the value of summer boating to the whitewater community. The safeguards developed on the advice of experts in 2007 will been maintained: weekend boating releases will be on consecutive days with no rampdown between days. Releases will not begin until the end of July, well after the movement of juvenile trout from tributaries into the mainstem NF Feather peaks around the end of June.


Fish on the Rock Creek reach are definitely doing better than they were before the Rock Creek – Cresta license was issued in 2001. There are more large trout in the Rock Creek reach today than there have been since surveys began in the late 1990’s.

The greatest limiting factor for trout on both the Rock Creek and Cresta reaches is summer water temperature. CSPA is currently addressing water temperature in the State Water Board’s Water Quality Certification proceeding for the Upper North Fork Feather Project, upstream of Rock Creek Reservoir. The next limiting factor for NF Feather River trout is lack of spawning habitat. The Rock Creek – Cresta ERC is continuing oversight of an artificial spawning channel, and of gravel augmentations in the NF Feather and selected tributaries. The ERC is also investigating tributary passage for fish and other aquatic biota under the highway and railroad that parallel the river. In addition, the ERC is overseeing a stream channel restoration on Yellow Creek, major tributary to the NF Feather and well-known stream fishery in its own right.

The North Fork of the Feather was once home of one of the premier trout fisheries of the west slope of the Sierra. Through its participation in the Rock Creek – Cresta ERC and other  hydropower proceedings, CSPA is working to restore the river so that it once again becomes a destination fishery.

[1] The Forest Service participates in the meetings and actions of the ERC, but maintains an independent status because of its authority over hydropower projects on National Forest land.

[2] No frogs have been detected on the Rock Creek reach for over ten years, and no population is known to have existed prior to that.

[3] See Table ES-1, p. ES-20: Hypothesis 12 states: “Total macroinvertebrate biomass will show a short term decrease.” Hypothesis was rejected. Comment:  “Results consistently showed increases or no overall change, although no result was statistically significant..” See also p. ES-21: Hypothesis 13 states: “Total macroinvertebrate biomass will show a long term increase.” Hypothesis was accepted. Comment: “The long term trend in biomass generally indicates an increase over time.”

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