Glenn is right on the water. It's been a very warm, dry week in the upper midwest. Our lawn is starting to show signs of heat stress.
Now is not the time to add fertilizer. Weeds have subsided, and if you didn't get a crabgrass preventer down in the spring, you might see that start to come on in a few weeks. Make sure to keep the grass watered...this is the best defense against a weak lawn and strong pests (both weeds and bugs).
Fertilizers aren't inherently bad for the environment. The problem usually stems from mismanagement...including poor application methods. Keep it off impervious surfaces (driveways, sidewalks, etc), where it is likely to runoff into the storm sewer and into lakes and streams. Keep it on the lawn. Read the directions carefully, and follow them. Even (and sometimes especially) animal manures can be harmful to the environment if mishandled. Fresh manure is often very high in soluble phosphorus and nitrogen...making it harmful to surface and groundwater when mishandled.