Rhode Island environmental officials say rust-colored patches in local waters pose no threat to public health.
The state Department of Environmental Management said Tuesday it has received reports of the patches, known as rust tide, in Narragansett Bay, Mt. Hope Bay and coastal salt ponds.
DEM says the rust tide is being caused by a large bloom of naturally occurring phytoplankton. This organism contains red photosynthetic pigments which cause the rust color visible on the water surface.
DEM says rust tide is not associated with the red tide that has caused shellfish closures in other New England states.
DEM says rust tide has been observed this summer in Peconic Bay off the eastern end of Long Island in New York and in Buzzards Bay and off Martha's Vineyard in Massachusetts.