A large oil slick that threatened New Jersey's Sandy Hook Bay had grown smaller by Friday.
The oil slick, which was 2 miles long and 400 feet wide on Thursday, had shrunk to 1 mile long and 50 yards wide.
Oil from the slick started washing up on parts of the shoreline Thursday afternoon, though the source of the spill was unclear.
Authorities worried the sheen could endanger the population of seals that migrate there each winter, the U.S. Coast Guard and parks officials told NBC 4 New York Thursday.
The Coast Guard worked into the night setting up a boom over a culvert in an effort to catch the oil before it could reach the environmentally sensitive, and popular horseshoe cove tidal marsh.
A spokesman for the agency said Friday that most of the remaining oil was expected to break up or evaporate by the day's first light because of the light nature of the petroleum involved in the slick.
Great and harbor seals are known to migrate to Sandy Hook Bay, and the National Park Service says the animals have already moved there for the season.
Officials at the Marine Mammal Stranding Center in Brigantine said the food supply for the seals could be compromised. If fish ingest the oil, the officials explained, and a seal eats enough of those fish, the seal could die.
Officials said the oil sheen also threatens the sea water intake pipe for the National Oceanic and Atmospheric Administration’s Fisheries lab on Sandy Hook.
The cause of the oil slick is under investigation.