Adult trout, too, love salmon eggs if the trout can get to them. But they do not find Onco in the gravel-covered redd. Aside from these natural hazards, the developing salmon egg has to survive some unnatural hazards. In another creek like Onco's, a mining dredge once ripped up the stream bed. Now, each year the loose soil releases silt which spreads far downstream.
Silt covers gravel and chokes off the oxygen supply in the water.
The eggs suffocate. Grazing cattle can trample the stream banks, their muddy footprints releasing even more silt. Pesticides applied to upstream crops can drain into a creek and poison fish. A road built alongside a stream can change the way water runs off. The stream is more apt to flood after a big rain.