The area between structures or hard surfaces and the water is a vital buffer zone, where shrubs and trees will prevent erosion and absorb runoff carrying phosphorus. Any water coming from driveways, roofs, or decks should be directed so that it can pool and settle into the soil, not run across the surface of the ground. Curve paths to the shore so water settles naturally instead of running straight to the lake, and use only permeable materials. When doing landscaping or construction, always use hay bales and other filtration barriers to trap any runoff or erosion. Near the shore, use no fertilizers if possible.
Liquid fertilizer is a better choice than solid.
If you limit the amount of lawn you have, you benefit the lake by reducing runoff and areas you might be tempted to fertilize, and you benefit yourself with reduced maintenance. If you are not connected to a municipal sewer system, pump your septic tank every two years. If your septic system was installed before 1974, it probably is allowing pollutants to reach the lake. The NH Department of Environmental Services can advise you. They may kill the bacteria your system needs to function properly, and can leach into the lake.