Suction dredging for gold involves the disruption of compacted stream beds and underwater gravel deposits by dislodging materials and sucking them through a tube attached to a gasoline-powered water pump. The 2-6 inch tubes employed by recreational suction dredgers act like underwater vacuums. The resulting silt and gravel slurry is then run through a sluice box or similar device to separate the waste material (spoils or tailings) from the heavier materials such as gold.
Similar to suction dredging, high banking or power sluicing draws massive amounts of water—more than 70 gallons per minute—from streams which is then run through a sluice. This amount of water—roughly 30 times the flow of your home shower—exits the sluice and under the best of circumstances heads to a retention pond where it ideally slowly percolates back into the waterway or water table. Unfortunately, many times these activities fail to operate ideally and silt-laden waters run directly in all cases they significantly alter areas that should act as vegetative filters for the streams they surround.
While the impacts of these activities on salmon and trout populations are myriad, the main impact types are:
Silt: Suction dredging and high banking directly and indirectly create silt problems in waterways. Human caused siltation impacts the ability of young salmon and trout as well as their invertebrate food base to breathe and survive.
Spoils and Tailings: Contrary to suction dredging lore, stream bed disruption and the associated piles of spoils or tailings do not enhance salmon and trout breeding habitat. In point of fact they do just the opposite as research indicates that salmon and steelhead preferentially use natural gravel beds over those created or modified by suction dredging. In addition, when they do use tailing survivorship of young salmon in these modified areas is compromised during high flow periods.
Rock Piles: Suction dredge operators tend to leave piles of large rocks that are too big to be processed in their machines. The movement of these rocks in the first place disturbs habitat needed by important food species such as caddis flies and other invertebrates. The piles themselves tend to compromise the function of gravel beds and also do not provide the same ecological benefits of naturally occurring formations. The persistence of these man-made rock piles over time is also a problem as these frequently are not removed by natural stream scouring.
Bank Destruction and Modification: Activities associated with suction dredging and high banking have been observed to cause significant bank disturbance either through destruction or modification of stream or river-side vegetation or through the facilitation of erosion through foot traffic or the movement of machines.
Associated Human Activities: Gold prospectors often camp along waterways and repeatedly use sites where they or others have had success or feel likely to achieve success. The associated concentration of human activity can cause localized impacts such as soil compaction and in-stream foot traffic as well as broader impacts associated with litter, fishing and the use of gasoline powered machinery in proximity to water.
The State of California has already imposed a ban on suction dredging. A moratorium went into effect in 2016 in Oregon, and efforts to craft regulations are ongoing. Washington is currently the "wild west" of suction dredging, having failed to implement any real permitting or regulation. The American Fisheries Society wrote a letter to California legislators prior to the moratorium being enacted in 2009 and in April of 2012 weighed in to the Oregon legislature as it considers suction dredging reform. Given the current state of Pacific salmon populations, we and our various allies in the angler, conservation, and environmental communities feel that activities such as suction dredging and high banking are simply not compatible with waterways occupied by recovering salmon and steelhead. We are currently working to create much needed reform of this reckless practice in Oregon and Washington. In addition, we are working with our partners to ensure that federal-level regulations and permitting requirements are being applied and enforced.
This is a big campaign, and we all need to work together on this issue to succeed. Cascadia Wildlands is currently working with a diversity of river stakeholders on this issue, including Klamath-Siskiyou Wildlands Center, Oregon Wild, Western Environmental Law Center, Trout Unlimited, Center for Biological Diversity, Mt. Rose Herbs, Caddis Fly and many more.
(Suction dredge mining can have a deleterious effects on the early life cycles of salmon and steelhead. Photo from Cascadia Wildlands archive.)