The NH Shoreland Water Quality Protection Act permits only low-phosphorus lawn fertilizers in the protected shoreland, and no fertilizer at all within 25 feet of the lake. The reason is that phosphorus is the limiting nutrient in NH lakes. More phosphorus leads to more algae, and more weeds. Fortunately, most NH soils have enough phosphorus already to grow good grass without adding any more. There's nothing lower than zero! And currently there are a lot of Zero phosphorus lawn fertilizers on the market. Look for a fertilizer with a zero middle number, for example 36-0-4 (Nitrogen-Phosphorus-Potash). Recently at Cyr Lumber in Windham we saw the following:
Scotts Super TurfBuilder with crabgrass preventer 36-0-4
Green Turf Winterizer 24-0-12
Ace Green Turf 29-0-3
Ace Green Turf with crabgrass preventer 36-0-4
Scotts 4-Step 32-0-12
If you mention at Cyr that you are from the Canobie Lake Protective Association, you'll get a 10 percent discount off the Scotts fertilizer.
Walmart and Dodge Grain in Salem also carry Zero phosphorus fertilizers, both Scotts and their house brands. They are likely available at other retailers, too.