The Great Lakes systemoffsite link includes five large lakes, one small lake, four connecting channels, and the St. Lawrence Seaway. The large lakes are Superior, Michigan, Huron, Erie, and Ontario. They hold about 90% of the freshwater in the United States and approximately 20% of the world's freshwater supply. Forty million residents of the United States and Canada depend on this system for clean drinking water.
Although NOAA is known for its work in marine habitats, our agency also monitors, studies, and protects many freshwater resources. NOAA satellites monitor the planet’s water supply, by mapping snow and ice fields and helping scientists predict where, when, and how much water will be available for humans to use. NOAA hydrologists provide river level forecasts to protect life and property and manage navigability of waterways. Many important fishes like salmon and sturgeon are anadromous, traveling between freshwater and saltwater throughout their life cycles. NOAA monitors and manages these fishes in partnership with local agencies. The Great Lakes, sometimes called our "third coast," are the foundation of a major coastal ecosystem. Though the lakes are freshwater, many of NOAA’s marine programs serve the region, including Marine Debris, National Marine Sanctuaries, Fisheries, The National Estuarine Research Reserve System, and others.
The water cycle is often taught as a simple circular cycle of evaporation, condensation, and precipitation. Although this can be a useful model, the reality is much more complicated. The paths and influences of water through Earth’s ecosystems are extremely complex and not completely understood. NOAA is striving to expand understanding of the water cycle at global to local scales to improve our ability to forecast weather, climate, water resources, and ecosystem health.