Which type of marks indicate the sides of channels as vessels approach from the sea?

Lateral marks are specifically designed to indicate the sides of navigation channels for vessels entering from the sea. These marks help boat operators understand where it is safe to navigate, providing visual guidance on the correct side of the channel to stay within. Typically, lateral marks are color-coded and often use a system of red and green colors, with red marks indicating the right side when entering a channel from the sea (preferred channel mark) and green marks indicating the left side.

In contrast, day marks are fixed structures that are primarily used as visual navigation aids during the daytime but do not serve to define the sides of a channel. Safe water marks are used to indicate that there is navigable water all around and are not specific to channel sides. Special purpose marks serve particular functions, such as indicating the location of moorings or underwater hazards, but do not denote channel limits. Thus, the specificity of lateral marks makes them the correct choice for indicating channel boundaries for vessels.