Two workers went missing when a boat sank in the Piyan River at Nayagangar Par in Goainghat upazila early Friday.   The identities of the missing people could not be known yet.   Abdul Ahad, officer-in-charge of Goainghat Police Station, said the incident took place around 2 am when the sand-laden boat carrying 11 workers sank in the river after being hit by another boat due to strong current in the river.   Nine workers managed to swim ashore with the help of local people while two went missing.   On information, drivers from local firefighting units went to the spot and started  a rescue operation.