The data from our Nabbing Nitrogen event show nitrogen levels are generally highest near the shore, suggesting land-based sources contribute to nitrogen pollution. Each dot on the map represents one water sample. The dots are color coded based on the Maine Department of Environmental Protection’s nitrogen advisory thresholds. Green dots show healthy levels of nitrogen. Yellow dots show nitrogen levels that can harm eelgrass habitat. Red dots show nitrogen levels that can lead to low amounts of oxygen in Casco Bay, which can lower water quality and harm marine life.