watermark. 1. A mark indicating the highest or lowest point to which water rises or falls.
high-water mark. 1. The shoreline of a sea reached by the water at high tide. • The high-water
mark is usu. computed as a mean or average high tide and not as the extreme height of the water. 2. In a freshwater lake created by a dam in an unnavigable stream, the highest point on the shore to which the dam can raise the water in ordinary circumstances. 3. In a river not subject to tides, the line that the river impresses on the soil by covering it long enough to deprive it of agricultural value. — Also termed high-water line.
low-water mark. 1. The shoreline of a sea marking the edge of the water at the lowest point of
the ordinary ebb tide. 2. In a river, the point to which the water recedes at its lowest stage.
2. The transparent design or symbol seen when paper is held up to the light, usu. to indicate the genuineness of the document or the document’s manufacturer.
[Blacks Law 8th]