Keep them out of storm drains and waterways.
Leaves are loaded with phosphorus. If they are not managed properly when they fall from trees in autumn, they can end up in surface runoff. When that runoff flows into waterways, the phosphorus in the leaves can cause algal blooms, lower the level of dissolved oxygen in the water, and kill fish and other aquatic organisms.
If you have a lot of leaves and leave them on your lawn, they can mat down and smother the grass over winter, leaving large bare patches that are vulnerable to erosion in spring.
Here are some leaf options that can help you have a healthy lawn while also protecting the environment:
If the leaves aren't too thick, simply mow them into fine pieces that are small enough to filter through the grass to the soil surface where they can help improve the soil. A mulching mower works best.
Collect grass clippings and leaves for composting. A mix of one part clippings to three parts leaves works well. Make sure your pile is located where the leaves won't blow or wash away. Turn the pile occasionally to speed decomposition. Use the compost in your garden and flower beds.
If you don't have a good place to compost leaves, bag them for collection by your local municipal composting operation.
The most important thing to remember is to keep leaves out of waterways. That means not raking them into the road where they can wash away, or into storm sewers where they can be carried into rivers and streams.