Having heard this allusion to flotsam and jetsam - and accustomed to seeing the occasional bit of seaweed when swimming in the Gulf of Mexico - I realized I hadn't a clear idea about the exact meaning of the terms. The frequency of the contemporaneous use of both words led me to further research. Though seemingly prosaic, the terms capture for me what is part of nautical poetry, not far removed for example from the allure of a compass, pier, ship's wheel or almost any other picture of maritime activity.
To get down to the point, in maritime law flotsam, jetsam, lagan and derelict are specific kinds of shipwreck.
"A wreck is categorized as property belonging to no apparent owner, that either sinks to the seabed or floats on the surface of the water, whether it be intentionally cast overboard or as the result of an accident. The term encompasses the hull of the vessel and its fixtures as well as any other form of object on board, such as cargo and stores and personal effects of the crew and passengers. This also encompasses the narrower definition of salvage, that is, property that has been recovered from a wreckage or the recovery of the ship itself."
Also known as "flotsan", the term "flotsam" (deriving from the word "float") refers to a sunken vessel whose goods float to the surface of the sea or any floating cargo that is cast overboard.
The term "jetsam" (deriving from the word "jettison") designates any cargo that is intentionally discarded from a ship or wreckage. Legally jetsam also floats, although floating is not part of the etymological meaning. Generally, "jettisoning" connotes the action of throwing goods overboard to lighten the load of the ship if it is in danger of being sunk.
Also called "ligan" (deriving from the Norse or Germanic word meaning "net fastened to the seabed" or the Latin word "ligare" meaning "to bind"), the term lagan refers to goods that are cast overboard and are heavy enough to sink to the ocean floor but are tied or otherwise linked to a floating marker such as a buoy or cork so that they can be found again by whomever marked the item. Lagan can also refer to large objects that are trapped within the sinking vessel.
Derelict can refer to goods that have sunk to the ocean floor, relinquished willingly or forcefully by its owner and thus abandoned but which no one has any hope of reclaiming. Generally a ship is defined as "abandoned" if there is no hope of recovery, known legally as "sine spe recuperandi" (which is the Latin phrase for "no hope of recovery") and this fact must be clearly proven by the salvaging party. It must also occur on navigable waters.
Similarly the terms embrace the alternate modus operandi of dealing with the predominant elements of one's own life, whether current events, thoughts or people; namely, losing them by accident or getting rid of them; hanging on if possible or admitting a lost cause. It is notable too that the legal entitlement to the objects of a shipwreck vary depending upon not only the particular manner of occurrence but also the jurisdiction in which the events transpire. Sufficient it is for my purposes to observe that the way one handles the casualties of life changes by virtue of many different factors; and, that there are ramifications to everything we undertake and do. It is somewhat spooky that the final frontier of salvation requires a navigable body of water, a stark reminder that not everything is capable of reclamation.
The precise meanings are lost in the common phrase "flotsam and jetsam" which generally describes useless or discarded objects. What remains constant however is that either of the terms flotsam, jetsam, lagan or derelict are the consequence of some misadventure or threat of misadventure - the winds and waves of daily living. While there is the overriding flavour of debris in any context there is nonetheless the possibility of worthiness upon closer examination. In every instance the feature of distress is apparent. The current environmental concern surrounding plastic debris is apt as well; even though recoverable, not all is dissolvable.