Great news, but sadly this is a widespread problem. Nearly all salmon rivers are affected in various degree by human intervention, whether it be through sewage pollution or agricultural runoff of macronutrients, both of which increase toxicity and cause deoxygenation of the streams due to bacterial growth. Rivers are also directly disturbed by being partially put under ground into pipes, often cutting the salmon off from the upstream breeding grounds. Lots of streams are also being used for hydropower, where dams either reduce or even fully stop the flow for periods of the year.

The good thing is that once conditions are restored, fish populations may rise quickly. However, it usually takes alot of work from locals, often cases this may be sport fishing clubs or even contracted by authorities, in continuing the efforts to yearly release smolt (juvenile salmon) in the rivers, in order to have them return to the same river later to spawn. Restoring previous populations takes time and effort!