Accumulations of nuisance drift macroalgae along the open coast Atlantic beaches of the Cape Cod National Seashore have been observed on an anecdotal basis for over 50 years. This entire stretch of coastline is sandy, with no solid substrata for algal attachment. During the summer of 2006, we collected data on drift macroalgal accumulations repeatedly throughout this National Seashore. Peak biomass (consisting of several filamentous red species and green algae, primarily Ulva lactuca) was found in early August, mainly at the northernmost site. Our data, together with ocean current patterns and anecdotal evidence, suggest that macroalgae may originate in rocky shorelines of northern New England and are transported south by Gulf of Maine currents. Algae are most likely caught along the Cape Cod National Seashore shoreline by sand bars, particularly in the northern part of the shoreline.