🔍 Key Concepts

• How vertical datums are used to reference charted depths and water levels • The specific standardized datum adopted for the entire Great Lakes–St. Lawrence system • Difference between a broad term like mean sea level and a specialized regional datum

💭 Think About

• Ask yourself which option sounds like an official, system-wide standard adopted for the Great Lakes and St. Lawrence River, not just a general geographic area or water level description. • Consider which name would most likely be used on NOAA or Canadian Hydrographic Service charts for that region. • Eliminate any choice that sounds more like a generic description of water level rather than a formally defined vertical datum.

✅ Before You Answer

• Check which option explicitly includes Great Lakes and suggests a formal, basin-wide standard. • Distinguish between a vertical datum name and a low-water reference that might be used for depths but not all water levels and benchmarks. • Recall what vertical datum name appears in official publications for Great Lakes water levels and benchmarks.