Plowing cropland contributes to soil erosion and buildup of sedimentation in streams, which tends to cover salmon spawning grounds. Application of fertilizers and other chemicals leads to the release of trace amounts of nitrates and pesticides into stream flows that may affect organisms that salmon feed on and the oxygen content in the water. Mike Wolf, water quality specialist with the Oregon Department of Agriculture, believes that improved crop management practices, such as the use of cover crops between plant rows to soak up fertilizer not used by the primary crop, will help keep nitrates from fertilizers out of streams. He agrees that soil erosion from farm fields into streams is harmful to salmon spawning habitat. Erosion control is an issue that agriculture is looking to improve in.
Farmers control erosion by using cover crops to stabilize the soil during winter rains.
They use reduced tillage methods to protect bare soil with a layer of crop plant residue. Taking water out of the stream for irrigation can also affect salmon. If so much water is removed from a stream that it becomes very shallow, the water temperature may increase, which is detrimental to juvenile salmon. Or, in extreme cases, if several irrigation demands are made on a stream at the same time, it may almost dry up completely. This can be very harmful to salmon if it happens while eggs or juveniles are in the stream.