sentences:  Some scientific diving is carried out by universities in support of undergraduate or postgraduate research programs, and government bodies such as the United States Environmental Protection Agency and the UK Environment Agency carry out scientific diving to recover samples of water, marine organisms and sea, lake or riverbed material to examine for signs of pollution.Equipment used varies widely in this field, and is generally selected based on cost, effectiveness, availability and risk factors.Open-circuit scuba is most often used as it is widely available and cost-effective, and is the entry level training mode in most places.