High water mark

[5] The debris is chiefly composed of rotting seaweed, but can also include a large amount of litter, either from ships at sea or from sewage outflows.

In parts of the United Kingdom, sandhoppers such as Talitrus saltator and the seaweed fly Coelopa frigida are abundant in the rotting seaweed, and these invertebrates provide food for shore birds such as the rock pipit, turnstone[6] and pied wagtail,[7] and mammals such as brown hares, foxes, voles and mice.

Federal regulations (33 CFR 328.3(e)) define the "ordinary high water mark" (OHWM) as "that line on the shore established by the fluctuations of water and indicated by physical characteristics such as a clear, natural line impressed on the bank, shelving, changes in the character of soil, destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider the characteristics of the surrounding areas.

For the purposes of Sections 9 and 10 of the Rivers and Harbors Act of 1899, the OHWM defines the lateral limits of federal jurisdiction over traditional navigable waters of the US.

In 2016, the Court of Appeals of Indiana ruled that land below the OHWM (as defined by common law) along Lake Michigan is held by the state in trust for public use.