They have been removing gravel from the lower vedder regularly since 1976. They don't have to get into the river . Gravel is removed from the islands that are formed when river is high or flooding. As you know the lower vedder narrows like a siphon from peach rd down to the hydro bridge. In December 1975 a log jam formed at the hydro bridge causing the water to back up and breech the railroad and flood yarrow. Below the hydro bridge the river is narrow also, and periodically needs the islands scalped. The set back dykes were built in 1976 to reduce the threat of secondary flooding . As for machines leaking oil into the water, they are inspected by the fisheries and if they are leaking oil are not allowed near the river. Removing these islands actually creates more spawning areas , removing finer scandal and gravel and exposing coarser gravel, that is better for spawning. More concern to pollutants . ( sewage , manure, and chemicals) that get into the rivers , than gravel removal. Look at the town of hope that removes the solids from sewage , and airates the liquids and then discharges it right into the Fraser. Theres lots of other towns up and down the Fraser that dump sewage into the Fraser also.