Use fertilizers on your lawn and garden sparingly and not immediately before a forecasted rain. Fertilizers can add excess nutrients to waterways. Those excess nutrients in nearby rivers can cause harmful algae to grow that steal oxygen and kill fish. The toxic conditions created by the algae blooms can limit human use and recreational enjoyment of local waters.
If you think your lawn needs fertilizer, have the soil tested first to determine the type of nutrients in your soil and where you really might be deficient. The K-State Soil Testing Lab and K-State Research and Extension provide soil analysis that can better help you care for your lawn.