Bulgaria on Sunday mourned its 15 citizens who drowned when their pleasure boat sank on Macedonia's popular Lake Ohrid, gathering at churches around the country and cancelling a national holiday. A total of 55 Bulgarian tourists were on board the Ilinden when it suddenly veered and sank in the waters of the deepest lake in the region and Macedonia's most popular tourist site on Saturday. Sofia cancelled Unification Day, a holiday usually marked by a grand army review in the central city of Plovdiv, with President Georgy Parvanov instead attending a mass for the victims in the city's cathedral. Masses were also held in other churches across the country. Monday has been officially declared a day of mourning in Bulgaria, while Macedonia called a day of mourning on Sunday. A team of Bulgarian pathologists arrived in Skopje on Sunday to assist their Macedonian colleagues in the autopsies of the victims and speed up the return of the bodies. A Macedonian investigating magistrate has ordered the boat's captain and owner, Sotir Filevski, 23, held for 30 days pending an investigation into the tragedy. Speaking to journalists on Sunday, Parvanov said that Macedonian investigators were investigating the possibility that the breaking of a metal cable linking the helm to the propeller caused the accident. He added that overloading of the ageing boat, made in 1924, was another possible cause as the ship was carrying 10 more people than its capacity. Fifteen Bulgarians, including a child, drowned in the accident involving what Bulgarian newspapers slammed on Sunday as 'a coffin boat.' The 24 Hours newspaper praised the swift rescue efforts of Macedonian campers on the lake and the Macedonian authorities 'who prevented a bigger tragedy.' Thirty-eight of the 40 Bulgarian survivors returned to Bulgaria on a government plane late Saturday and eight of them were hospitalised with minor injuries, Health Minister Bozhidar Nanev said. A Bulgarian army plane was on standby to immediately leave for Macedonia and fly the bodies of the victims home, once the Macedonian authorities release them for burial. All those who drowned in the accident came from the same region, east of Sofia. A list of their names released by the government showed that whole families had perished. Eight of the 15 victims were from the central village of Anton, where authorities declared three days of mourning starting Sunday. 