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Diamond Lake Recovery – Again

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Diamond Lake Recovery – Again New Approaches Diamond Lake Recovery – Again Joe Eilers and Holly Truemper Lake Description the balance used to stock lakes throughout fishing. In this same year, ODFW began iamond Lake is a stunningly the state. Although two permanent streams the practice of supplementing the stocking beautiful 1,226 ha lake located enter Diamond Lake, both are derived of fingerlings with legal-sized trout to just 18 km north of Crater Lake. from spring water so cold that they don’t maintain a fishery. The initial attempt It is flanked by Mt. Thielsen on support much trout reproduction. by ODFW to proceed with a rotenone Dthe east and by Mt. Bailey on the west. project, much as was conducted in the In a draft of the park boundary, Diamond Collapse of the Trout Fishery 1950s, was aborted when opposition Lake was included with the national park This scenario of trout egg collection/ to the treatment caused the project to to provide a complementary experience to rearing/restocking worked well until the be shelved. However, opposition to a the breathtakingly beautiful, but difficult 1940s, when fish biologists noticed that repeated rotenone treatment quickly to touch Crater Lake. However, the final growth, survival, and harvest of rainbow dissipated after the summer of 2001 when wrangling resulted in Diamond Lake trout began to mysteriously decline. the lake was hit by an intense bloom of staying with the Umpqua National Forest Multiple hypotheses were investigated Anabaena. In addition, with zooplankton and developing into a more intensive until the biologists realized that the trout grazers being eaten by the tui chub, there recreational resource than might have were being out-competed for their prey, was little control of the algae. However, occurred otherwise. There is a large zooplankton and benthic invertebrates, it was found that the excretion of nitrogen privately run lodge, 445 Forest Service by an invasive small minnow, the tui and phosphorus by the large population campsites in several campgrounds, and chub (Gila bicolor). The tui chub was of tui chub provided the primary 102 private cabins on land adjacent to believed to have entered the lake via nutrients to sustain the cyanobacteria the lake leased from the Forest Service. live bait dumped into the lake after a blooms. With lake closures from the This lineage factors into its current days’ fishing. Biologists tried netting cyanobacteria blooms, recreational use management challenges. the chub and using spot-treatments of declined dramatically and economic Diamond Lake was formed by tephra rotenone until they concluded that they impacts to the local economy took their erupting from Mt. Mazama (now the site would have to eradicate the tui chub. The toll. It only took several years of the of Crater Lake) about 6,700 years ago. original Diamond Lake recovery project blooms before resistance to the proposed The ash and volcanic debris impounded consisted of dredging a channel to lower rotenone treatment faded and planning a stream in a mountain meadow leaving the lake stage by 2.4 m and applying for a project at the lake resumed with the a lake that was about 6 m deeper than powdered rotenone in September 1954. goal of restoring the lake to fishable and its current condition. The lake remained The lake was restocked and fishing was swimmable. fishless until about 1910 when trout opened up again in spring 1956 and trout were first introduced. The shallow lake fishing continued successfully for over The Rotenone Treatment (Zmax= 14.8 m; Zmean= 6.9 m) supported three more decades. Additional details on In the 1950s, project planners didn’t a productive benthic fauna and probably the lake history are available elsewhere have to contend with environmental a high density of large cladocerans (Eilers et al. 2001; 2007). impact statements (EISs). Following and copepods often found in many In 1992, fish biologists once again completion of this tome for the current fishless lakes in the Cascade Range. found tui chub in the lake. Although project, plans began for a repeat of the The introduced trout grew rapidly and it was intensely disappointing to see rotenone project (Umpqua National Forest for a period this was one of the largest their nemesis in the lake again, it also 2004). With relatively modest changes fish egg collection stations in the region, served to explain the decline in the to the original treatment design, the 20th with collections of over 18 million eggs. trout fishery, which in retrospect, was century version of the Diamond Lake This bounty allowed the Oregon Game beginning to be expressed in the late Restoration Project was launched. The Commission, predecessor agency to the 1980s. From 1992, when the tui chub original canal was re-dredged to allow for Oregon Department of Fish & Wildlife were first encountered until 2001, the the drawdown that served three functions: (ODFW), to rear 1 million of the young only obvious sign that something was (1) reduce the lake volume by 40 percent, trout for planting back into the lake with clearly wrong with the lake was the poor thus reducing the amount of rotenone Summer 2010 / LAKELINE 23 required; (2) allow for water to be held spray the liquid rotenone plied the shallow meter, exceeded densities of over 75,000 in the lake following the treatment, waters along the shoreline (Figure 2). individuals per cubic meter by the end thus allowing the rotenone to degrade Finally, nine large pontoon boats built for of June 2007. The biomass of benthic before water was released downstream; the project applied rotenone behind their organisms showed a similar response and (3) reduce the area of the lake with crafts (Figure 3). In the end, 32.6 metric with numbers increasing from 2.3 g/m2 macrophyte coverage and thus increase tonnes of liquid rotenone and 48.6 metric before the treatment to 22.5 g/m2 in 2007, the likelihood for a complete kill of the tonnes of powdered rotenone were applied 18.8 g/m2 in 2008, and 38.3 g/m2 in 2009. fish (Figure 1). The water was drawn to the lake to achieve a concentration Species of benthic macroinvertebrates, down through the new headgate over a of 0.11 ppm of active ingredient in the which had been absent for years, returned nine-month period to minimize hydraulic water column. All fish cages deployed rapidly, although new benthic species overload to the outlet stream. Tui chub throughout the lake indicated that the kill are still being observed annually. Fish were netted from the lake in the summer had been complete. growth returned to phenomenal levels of 2006 to reduce the additional nutrient with growth rates of 4.3 cm/mo in the first load from the mass of fish that would Lake Response to Rotenone summer following the treatment, 4.7 cm/ decay in the lake following the treatment. The initial response was mo in 2008, and 3.4 cm/mo in 2009. The This resulted in removal of 30.8 metric anticlimactic, although weather conditions fish were fat, creels were full, and local tonnes of tui chub. Finally, the rotenone were favorable for mixing the rotenone cash registers rang announcing resurgence was applied on September 13-15, 2006. throughout the lake. A relatively small of the local recreation-based economy. The first applications started by metering number of fish struggled to the surface The Anabaena that had plagued the liquid rotenone at drip stations into the and expired, but for the most part, lake since 2001 virtually disappeared, two tributaries to drive any tui chub that nothing much happened. Several days replaced by low densities of might have wandered into the cold inlet later fish began to decompose, float cryptomonads and diatoms. Secchi disk streams. The next sequence involved to the surface, and accumulate on the transparency, which before treatment use of applicators on foot equipped with shoreline, revealing the true magnitude averaged about 1.6 meters in the summer backpack units dispersing liquid rotenone of the dominance of the tui chub (Figure prior to treatment, reached a maximum along the shoreline. Simultaneously, 4). During post treatment, another 15.9 of 12.5 m in June 2007 (Figure 6). Light smaller boats equipped with pumps to metric tonnes of fish were raked up and now reached the entire lake bottom. disposed offsite. However, many As a consequence, aquatic plants (both of the dead tui chub simply macrophytes and filamentous algae) decayed in the lake, fueling a colonized some areas of the lake that vigorous Anabaena bloom that formerly were light-limited. Epilimnetic continued despite the declining pH, which had averaged 9.5 in 2006, lake temperatures (Figure 5). declined to an average of 8.4 in 2007 and Rotenone and its immediate 7.8 in 2008. Chlorophyll concentrations, degradation product rotenolone which had averaged 15.3 ug/L prior to were no longer detectable about treatment, now averaged 2.7 ug/L in eight weeks after treatment, 2007 and 7.8 ug/L in 2008. The lake making it possible to open was meeting water quality standards for the headgate. The process of the first time in years. All this occurred refilling the lake began and was without significantly altering the nutrient finally achieved in July of 2007. concentrations in Diamond Lake. What Conditions in the lake caused had changed was the rate of nutrient concern as oxygen continued to re-supply made possible by the abundant be consumed in waters below 6 tui chub. Diamond Lake became the only m and cyanobacteria still thrived lake to meet its TMDL targets by reducing below the thickening ice layer.
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