Jetsam has an extended use outside of maritime law and it can be used for anything washed up on the shore.
In extended use. Something washed up or discarded; refuse, detritus. - OED
However, the news articles usually use the phrase flotsam and jetsam for the debris washed up on the shore.
The foul-smelling haul of flotsam and jetsam included plastic containers, bin liners stuffed to bursting and even a pile of cattle bones reached 30m inland. - telegraph.co.uk
A recent stroll along a Bay of Islands beach included the ugly sight of plastic bag remnants tangled all through the tide line flotsam and jetsam. - stuff.co.nz
Wikipedia offers the terms beach litter and tidewrack in the marine debris article:
Floating oceanic debris tends to accumulate at the center of gyres and on coastlines, frequently washing aground, when it is known as beach litter or tidewrack.
Tidewrack is not that common and it is not defined in big dictionaries; but it has this definition in Wiktionary:
seaweed and similar marine vegetation and rubbish deposited along a shore by a receding tide
The more common term is simply wrack but it is mainly used for the biological debris.
a. Marine vegetation, seaweed or the like, cast ashore by the waves or growing on the tidal seashore. (Cf. wreck n.1 2, varec n. 1)
Also cart-wrack, grass-wrack, kelp-wrack, lady-wrack, sea-wrack.
b. Weeds, rubbish, waste, etc., floating on, or washed down or ashore by, a river, pond, or the like; = wreck n.1 2b.
Image source: www.beachapedia.org
Another similar term is wrack line.
In the marine sense, the wrack line is the line of debris left on the beach by high tide. The wrack is usually made up of eel grass, kelp, crustacean shells, feathers, bits of plastic, and all kinds of litter.