Hundreds of artists, collectors and curators have gathered in Mali to celebrate one of Africa's biggest photography exhibitions, Bamako Encounters. Ecological concerns are a major theme this year. This work is from the series A Vanishing Wetland by Nigerian artist Akintunde Akinyele.The main exhibition is called For a Sustainable World and takes place at the National Museum of Mali. This photo is from the series Djoliba and The River People by Raymond Dakoua, from Ivory Coast.South Africa's Pieter Hugo won the top prize, the Seydou Keita Award, with his series Permanent Error which includes this photo taken at Agbogblishie Market in a slum in Ghana's capital, Accra, in 2009.This is one of a series of portraits of the Turkana people in north-west Kenya by Jehad Nga, an artist who was born into a Libyan family in the United States and has worked extensively in East Africa. Mr Nga won the jury's prize.The pan-African show puts together the works of 45 photographers and 10 video artists from 27 countries. This picture, The Tree of Life, is by Arturo Bibang, from Equatorial Guinea.Fatoumata Diabate is one of Mali's most accomplished young photographers. This is from her series L'Homme en Animal. She is one of the 12 artists selected to represent the Bamako Encounters at the international fair Paris Photo, later this week, which this year pays hommage to photography from sub-Saharan Africa.Senegal's Victor Omar Diop imagines the future in his series Fashion 2112, the Elegance of the 22nd Century. This work is called Thirst. Several of the photos in the exhibition allude to the problems related to water scarcity in parts of Africa.This photo by Ghana's Nyani Quarmyne, from his series Climate Change, won the prize of the European Union together with Burkina Faso's Nyaba Leon Ouedraogo. The exhibition's artistic directors are two women, Tunisian-born Michket Krifa and Italian Laura Serani.Another woman, Cameroon's Ruth Belinga, was given the green light to organise a show of her choice. She presented the video work of her compatriot Goddy Leye. The organisers also invited several artists from North Africa who have covered the Arab Spring, including Lofti Ghariani from Tunisia.The exhibition's general director, Samuel Sidibe, who is also the director of the National Museum of Mali, told BBC Africa that they want to create a professional network of African curators and art critics. This picture by South Africa's Sabelo Mlangeni shows people watching a football match during last year's World Cup.The National Museum is undertaking a project to preserve the country's photographic heritage, starting with the digitalization of hundreds of negatives by three artists: Soungalo Male, Abderramane Sakaly and Malick Sidibe. This photo by Soungalo Male is from 1960.Malick Sidibe is considered one of the continent's greatest photographers. In 2007 he was awarded a Golden Lion for Lifetime Achievement at the 52nd Venice Biennale. At the opening of this year's Bamako Encounters he was decorated by the French government as an Officier of the Order of Arts and Letters.Parallel to the main exhibition there are several other shows all over Bamako, including one by students from Mali's Conservatoire des Arts et Metiers Multimedia, one of Africa's best art universities. This work is by Zimbabwean Tsvangirayi Mukwazhi, from the series Granite Mining in Angola.A work by Francis Kodia from Congo-Brazzaville. The African Photography Biennial, also known by its name in French, Rencontres de Bamako, runs until 1 January 2012. Paris Photo takes place at the French capital's Grand Palais from 10 - 13 November 2011.