Everything shaded in blue on a navigation chart indicates what depth?

On navigation charts, areas shaded in blue typically indicate water depths that are generally considered to be less than 30 feet. This convention is widely used in nautical charting to help mariners quickly assess the depths of water in a given area and to identify safe navigation routes, especially in coastal waters and regions where shallow depths could pose a risk to vessels. The specific depth range allows mariners to make informed decisions about whether it is safe for their vessel to navigate through certain areas. Knowing that blue areas signify depths less than 30 feet is crucial for ensuring safe passage and avoiding grounding.