Another expedition ship has run aground in the frigid waters of Antarctica. Quark Expeditions' 68-passenger Ocean Nova is stuck in Antarctica's Marguerite Bay, west of Debenham Island and near the Argentine research station San Martin, 550 nautical miles (about 1,000km) south of the Chilean base of Frei, when approaching the Mac Clary glacial. No casualties have been reported. The vessel is safe and there is no risk to the passengers and crew, the Argentine Army said. The Argentine and Chilean armies are assisting in rescue operations, military sources said. The cause of the accident is yet to be determined. A Spanish vessel of Oceanographic Investigation (BIO) Hesperides and another from Clipper Adventure Transport are also at the scene to assist in rescue operations. The 240 feet (73 meters) Ocean Nova was built in Denmark. It was carrying passengers from 22 different countries who were on their eighth day of a two-week expedition to explore the polar circle. The incident comes just two months after another expedition ship, the 84-passenger Ushuaia, ran aground near the entrance to Antarctica's famed Wilhelmina Bay. The Ushuaia eventually was evacuated before being freed by a Chilean tugboat.