Because of their fragile nature, marine snow--sized aggregates (aggregates >0.5 mm in longest dimension) have been generally overlooked in shallow-water environments. We report in situ observations and measurements in Cape Lookout tight, North Carolina, that indicate that marine snow is probably always present and usually abundant. Underwater photographs show that over a period of hours, marine snow varies in size from 8 to 71¿10-5 mL and in abundance from 291 to 489 L-1, but that such variations in size and abundance are not obviously related to tide, total suspended sediment concentration, or current speeds in the 10 to 20 cm s-1 range. Photographs and concurrent transmissiometer records suggest that variations in size, shape, and abundance of marine snow may be sufficiently great that particulates do not remain optically constant and thus affect beam transmission, irrespective of total suspended-sediment concentration levels. Marine snow is significant geologically in that it has high setting rates (50 to 200 m per day) and may be the package in which much of the vertical mass flux occurs. If so, it offers an explanation for the high accumulation rates observed in coastal and estuarine fluid mud deposits. ¿ American Geophysical Union 1987