Natural seeps and springs have dried up. Rain hits roofs, rain gutters and parking lots, then flows into storm sewers and is channeled out into the sewage system, then into the rivers. Flood control structures such as dikes and berms prevent water from following its natural course on river floodplains. Petroleum products, air pollution byproducts, lawn and garden chemicals, sewage and other urban dirt gets picked up by rainwater and flushed into our rivers. People illegally dispose of household chemicals down storm drains.
Construction sites send large amounts of sediment into the waterways in the rainy season.
When we cut trees for views and development, we remove the cooling shade along urban waterways. With increasing needs for urban drinking water, we take water out of salmon habitat for human needs. The more water we take for urban use, the less is left for salmon. We have no quarrel with it. They are going extinct.