The sounding numbers show the water level at ____________ ___________ tide.

The sounding numbers indicate the water level at mean low tide because these measurements are taken based on average conditions over time. Mean low tide represents the average of all low tides observed at a particular location over a sufficiently long period, typically 19 years. This is useful for navigation, as it provides a consistent reference point for mariners to assess water depth and avoid grounding.

Mean low tide is especially important for determining safe depths in navigable waters, as it reflects the lowest expected water level, helping vessel operators understand the minimum water depth they can safely navigate. By relying on mean low tide, boat crew members can plan their routes and activities with greater accuracy, ensuring safety on the water.