Many of our garden amendments and chemicals are designed to leach. If they didn t leach, they wouldn t enter the soil. And product directions have you apply quantities that ensure enough stays behind in the local soil to do some good for the garden. The rest leaches on through and enters the water system. Insecticides, herbicides and fertilizers all have impact on salmon habitat.
Insecticides have two impacts.
The most direct is the toxic effect of many insecticides on fish. Although product labels warn of fish toxicity, we usually don t pay much attention if we don t have a fish pond. Some studies suggest that diazinon seldom migrates below the top inch of soil, but other studies have found it in wells in California and tap water in Ottawa and Japan. Studies of disulfoton claim that it strongly bonds to soil, and most groundwater samples have not found it, although it has been found in groundwater studies in California. The second impact of insecticides is by killing or reducing populations of insects that would normally be food for the hatchlings.