Anything we do on land eventually affects the streams, rivers, lakes, and the ocean because the runoff takes into the water pollutants, chemicals, fertilizer, pesticides, animal droppings, and so on.
The most obvious ways we can help are to pick up after our animals; not to pour oil or paint or other hazardous materials into the storm drains—in the Washington area, whatever is dumped into a storm drain eventually ends up in the Cheapeake Bay to the detriment of fish and wildlife; and not to use environmentally unfriendly fertilizers, weed killers, and pesticides.
Gaining in popularity are watershed friendly gardens that make use of native plants and trees, composting, nonharmful chemicals, and various other practices to conserve water in the garden itself, and to ensure that any runoff is not going to harm the local watershed. Such landscaping also creates an inviting habitat for wildlife.
This summer, Arlington County held a Watershed Friendly Yard Tour, and the owners of this house were proud participants.