The truth of it is that most of those places that suction dredges are working are spots that have already been mined in the past , also miners already have rules to follow and are already restricted by the time of year open to dredging . Also what these guys are doing is not in spawning areas , they are targeting bedrock and deep pools where gold has fallen out of the water column during a storm , so the rocks and gold and small pieces of quartz are in the cracks of the bedrock and they basically suck them out of the crack. Run the product through the sluice and leave clean gravel and stones up on the shore after its been run , there is not much silt because of where they are running and the hydrology of the river , small fish will be attracted to the flow coming off the sluice and will pick off biologicals that result from cleaning the paydirt.