There aren't many things more depressing than walking on a beautiful beach and discovering a stretch of it that's covered in detritus. Detritus means trash or debris.
Usually, detritus refers to waste or junk of some kind, but it can actually mean any accumulation of material, not only man-made stuff. Loose gravel, silt, and sand can all be called detritus, and so can decomposed organic matter, like piles of dead leaves. The Latin word detritus literally means "a wearing away."