Harbormaster is a person usually having the experience of a certificated master mariner and a good knowledge of the characteristics of the port and its whole area. A harbor master administers the entire shipping movements that take place in and within reach of the port s/he is responsible for. They are also responsible for issuing local safety information and may oversee the maintenance and provision of navigational aids within the port, co-ordinate responses to emergencies, inspect vessels and oversee pilotage services. A harbormaster may sometimes have legal power to detain, caution or even arrest persons committing an offence within the port or tidal range of the port's responsibilities. A harbormaster may investigate acts including criminal acts, immigration, customs and excise, maritime and river safety and environmental and pollution issues.