The sediment plume below suction dredge operation can have mercury concentrations exceeding water quality standards, creating a health hazard for fish, wildlife, and humans.īased on impacts documented in the scientific literature, we believe that suction dredge mining poses a threat to the state’s salmon strongholds, including the Illinois, North Fork John Day, and Wenaha. Although suction dredging captures some mercury from the streambed, much of the mercury is washed downstream. Suction dredge mining uncovers hazardous forms of mercury left over from historical mining practices. Suction dredge mining can release hazardous forms of mercury. Studies have documented a reduction in aquatic insect communities in areas affected by suction dredge mining in comparison to those areas not affected by mining. Fine sediments can also decrease the abundance of aquatic insects, a major prey source for juvenile fish. Fine sediments impact fish habitat by filling in the crevices between boulders and cobbles that otherwise provide cover for juvenile salmon and trout, and by smothering spawning gravels with sands and silts that prevent adequate oxygen from reaching incubating eggs. Suction dredge mining can result in levels of fine sediments (silts and sands) in downstream habitats that are as high as 10 to 20 times above normal background conditions. Suction dredge mining increases sedimentation in downstream fish habitats. It is also important for bull trout, a federally listed species that spawns in very cold streams and whose eggs and larvae can remain in the streambed into summer. This is particularly important for species like cutthroat trout and steelhead that spawn in late winter and whose eggs may incubate into summer. Suction dredge mining results in direct mortality to incubating eggs and juvenile fish.Įggs and juvenile fish suffer high mortality when vacuumed into suction dredges. These effects can occur well after suction dredge mining activity has ceased. Spawning gravel that has been disturbed by suction dredge mining is known to erode at a higher rate than in undisturbed areas, thereby washing away and killing incubating salmon eggs. Where dredging vacuums up streambeds, it destabilizes the streambed gravels that salmon use for spawning. Suction dredge mining reduces the reproductive success of Pacific salmon. The amount and quality of cover habitat in streams is a key factor in the productivity of many of Oregon’s salmon and trout populations. Cover habitat is essential for juvenile salmon and trout as they avoid predators and avoid being washed downstream during winter floods. Suction dredge mining disturbs key habitat for juvenile salmon and trout.īy removing or displacing cobbles, boulders, and logs, suction dredge mining impacts important cover habitat for juvenile salmon and trout. Here are some of the key research findings on suction dredging relevant for Oregon’s salmon, steelhead, and trout populations: TAKE ACTION! Ask your elected leaders to support the Suction Dredge Reform Bill (SB 3-8) to protect clean water and native fish! There’s also potential for impacts to human health, as legacy mercury from historical gold mining in streams is remobilized into waters used for drinking and recreation. Studies demonstrate negative effects on streambed scour, fish habitat, and direct mortality of federally-listed fishes. The impacts of suction dredge mining on stream habitat, fish, and other wildlife are well documented in science publications. Now, the Oregon Legislature is considering a permanent solution. The recent spike in suction dredge mining in Oregon caused the state to put a temporary ban on the practice. California banned the practice in 2009, sending miners north into Southern Oregon. Suction dredge mining is practiced by recreational miners who vacuum up streambeds in search of gold. With a bill to reform suction dredge mining making its way through the Oregon Legislature, our science director details the mining practice’s harmful impacts.
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