A high water mark is a point that represents the maximum rise of a body of water over land. Such a mark is often the result of a flood, but high water marks may reflect an all-time high, an annual high or the high point for some other division of time. Knowledge of the high water mark for an area is useful in managing the development of that area, particularly in making preparations for flood surges. High water marks from floods have been measured for planning purposes since at least as far back as the civilizations of ancient Egypt. It is a common practice to create a physical marker indicating one or more of the highest water marks for an area, usually with a line at the level to which the water rose, and a notation of the date on which this high water mark was set. This may be a free-standing flood level sign or other marker, or it may be affixed to a building or other structure that was standing at the time of the flood that set the mark.

Talitridae is a family of amphipods. Terrestrial species are often referred to as landhoppers and beach dwellers are called sandhoppers or sand fleas. The name sand flea is misleading, though, because these talitrid amphipods are not siphonapterans, do not bite people, and are not limited to sandy beaches.